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William M. Walter Jr., Betsy Randall-Schadel, and William E. Schadel

Wound healing in cucumber fruit (Cucumis sativus L., cv. Calypso) was studied using histological and degradative techniques. A thick exudate appeared at the wounded surface shortly after wounding. This material retarded water loss and possibly aided in the formation of sclerified parenchyma observed 24 hours after wounding. The sclerified material was positive to a modified Weisner stain, indicating lignification was occurring. Wound periderm (cork) was initiated directly beneath the sclerified parenchyma cells within 48 hours after wounding. The cork layers were positive to Sudan IV stain, indicating suberin was being formed. The rate of phellem development decreased by 6 days after wounding. By day 7, younger phellem cells and sclerified parenchyma cells were stained by Sudan IV. Degradation of the wound tissue by chemical procedures demonstrated that relatively large amounts of lignin and suberin were deposited during healing. Fragments from the lignin degradation Indicated that lignin was composed mainly of gualacyl and p-hydroxyphenyl residues. Suberin was found to contain mainly 1,16-hexadecane and 1,18-osctadecene decarboxylic acids detected as the silylated diol derivatives.

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Kay P. Gersch, Carl E. Motsenbocker, and Gregory A. Lang

-28-0097. We gratefully appreciate the assistance of Raoul Machiavelli with statistical analyses and the technical assistance of Cheryl Crowder and the staff of the Louisiana State Univ. Veterinary School Histology Laboratory, Baton Rouge. Appreciation is also

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J.T.A. Proctor, T. Slimmon, and P.K. Saxena

Ginseng is an herbaceous perennial that grows in the understorey of deciduous hardwood forests and is also cultivated for its highly valued root. The primary method of propagation of ginseng is by seed which requires the breaking of dormancy by stratification, a process which takes 18–24 months. Investigation of factors controlling the growth and development of ginseng plants is a prerequisite to the development of a more efficient system of ginseng propagation. We have recently modulated the morphogenetic potential of geranium roots and stimulated de novo development of shoots and embryo-like structures which later formed whole plants using thidiazuron (TDZ). Our objective was to investigate the morphological changes in seedling and mature ginseng plants induced by TDZ, particularly in relation to root and shoot morphogenesis and economic yield. Applications of TDZ (0.22 and 2.20 ppm), either as foliar sprays or soil watering to greenhouse-grown seedlings over 18 weeks (2 weeks after sowing to 20 weeks when plants were harvested) induced similar effects. These responses included increased stem length and diameter, and shoot and root weight (economic yield). Single foliar applications of TDZ at 62.5 and 125 ppm to 3-year-old field-grown ginseng plants 3 months before harvest increased root biomass (economic yield) by 19% to 23%. Roots of TDZ-treated seedlings and 3-year-old field-grown plants developed thickened secondary roots on the upper part of the taproot. The root-like structure of these secondary roots was confirmed by histology. In addition, TDZ treatments induced adventitious buds on the shoulder of 3-year-old roots. These buds developed into shoots to give multi-stem plants following a period of dormancy, which was overcome with GA3 (gibberellic acid) treatment before planting.

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Mary Jean Welser and Martin C. Goffinet

Grapevine yellows is a destructive, worldwide disease of grapevines that is caused by a phytoplasma, a bacterium-like organism that infects and disrupts the vascular system of shoots. The North American form of grapevine yellows (NAGY) has been observed in New York State since the mid-1970s and in Virginia since the mid-1990s. Symptoms duplicate those of vines suffering from an Australian disease complex known as Australian grapevine yellows (AGY). We sought to determine if infected `Chardonnay' vines have common anatomical characteristics across the three regions. At each geographic site in late summer, 2003–04, leaf and internode samples were taken from younger green regions of shoots and from mature basal regions in the fruiting zone. These were processed for histology. The anatomy of each organ type was compared between locations on the shoot, between geographic locations, and between affected and normal shoots. The phloem was the only tissue universally affected in vines with NAGY or AGY symptoms. In stem internodes, both primary phloem and secondary phloem showed many senescent cells, abnormally proliferated giant cells, and hyperplasia. In affected secondary phloem there was disruption of the radial files of cells that normally differentiate from the cambium into mature phloem cell types. Normal bands of secondary phloem fibers (“hard phloem”) in internodes were weak or absent in affected vines. Leaves also had disrupted phloem organization but near-normal xylem organization in vines with symptoms. Leaves of infected vines frequently showed a disruption of sugar transport out of the leaf blades, manifested by a heavy buildup of starch in chloroplasts of mesophyll cells and bundle-sheath cells.

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Alessandro Abruzzese, Ilaria Mignani, and Sergio M. Cocucci

Apple (Malus domestica Borkh.) trees are often affected by a severe June fruit drop, which is often correlated with competition phenomena involving fruit nutrition. This research was initiated to determine if June drop in `Gloster'/M.9 apple could be correlated with a diminished nutrient availability in developing seeds and fruit. During the test period [30 to 62 days after full bloom (AFB)], the fruit that abscised had a diameter similar to that reached by persisting fruit 13 days earlier. Biochemical parameters related to nutritional status of fruit were measured when an abscission peak occurred 38 days AFB. Persisting fruit (control) and abscised fruit were compared along with fruit that abscise 13 days later. The cortex tissue obtained from the two kinds of abscised fruit showed a higher level of soluble reducing sugars and sucrose and a lower content of K+, acid hydrolyzable polysaccharides, and protein compared to the control. Further, the Ca2+ content was higher in abscised fruit than in controls of the same age, whereas there was no difference when fruit of the same size were compared. Total amino acid level was similar in control and abscised fruit at the same age, but there was a lower amino acid level in abscised fruit of the same size. Histological analysis of cortex tissue indicated that abscised fruit have larger cells with less evident nuclei and thinner cell walls than controls. Compared to control fruit, abscised fruit showed the same average number of seeds and a severe inhibition of seed growth; seeds from both kinds of abscised fruit had the same or higher levels of the parameters measured. No positive correlations were observed between fruit abscission and nutrient content of seeds or fruit.

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Benoît Bertrand, Hervé Etienne, and Albertus Eskes

In order to avoid nematode damage to roots of Coffea arabica L. in Latin America, a common practice is interspecific grafting on C. canephora var. Robusta (Pierre) rootstocks. The performance of two C. arabica cultivars, `Caturra' and `Catimor T5175', was evaluated on four rootstocks: C. canephora var. Robusta (`T3561' and `T3757') and C. liberica var. liberica (Hiern) and var. dewevrei (Lebrun), over 5 years in a trial at 1180 m elevation in Costa Rica. Nongrafted plants of the two Arabica cultivars were used as controls. Mortality of plants grafted on the two C. liberica cvs. was >20% vs. 6% to 13% for plants grafted on C. canephora, and 3% to 4% for the two controls. Analysis of accumulated yields over four harvests showed that the rootstocks limited stem girth and reduced yield 10% to 48%. Yield on the C. canephora rootstock was greater than that on the two C. liberica cultivars. However, grafting did not affect female fertility (peaberries, empty berries) or content of several chemicals, such as caffeine, fat, and sucrose. The two C. liberica rootstocks significantly reduced aroma and bean size. Histological studies revealed symptoms of incompatibility, characterized by more dilated and less distinct growth rings and appearance of plugged vascular connections. The poor performance of the rootstocks may therefore be explained by partial incompatibility. However, growth and productivity were also affected by poor adaptations of C. canephora, C. liberica, and C. dewevrei to the lower temperature at high altitudes and by morphological differences in the root systems. These results emphasize the need to develop better adapted rootstock cultivars from C. canephora var. Robusta.

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Michael Olszewski, Wallace Pill, Thompson D. Pizzolato, and John Pesek

Germination studies indicated that increasing priming duration (-1.0 MPa at 20 °C for 7, 14, or 21 days) increased `Moss Curled' parsley [Petroselinum crispum (Mill.) Nyman ex A.W. Hill] germination rate quadratically and seed moisture content linearly. A histological and anatomical study was conducted to identify and/or quantify principle mericarp organ or tissue volume changes influenced by priming duration. Embryo volume increased as priming duration increased from 7 to 21 days (0.014 to 0.034 mm3), and this was due more to radicle (0.007 to 0.022 mm3) than to cotyledon (0.006 to 0.011 mm3) growth. Concomitant with increased embryo volume was increased volume of the depleted layer (space formation, surrounding the embryo), from 0.038 after 7 days to 0.071 mm3 after 21 days, and increased hydrolysis of central endosperm (a thick-walled endosperm type). In nonprimed mericarps, central endosperm cells constituted 97% of the endosperm volume. The remaining 3% was comprised of 1% depleted layer and 2% distal endosperm (small, thin-walled, and irregularly shaped endosperm cells). During 7 or 21 days of priming, ≈10% or 40%, respectively, of central endosperm cells were hydrolyzed centrifugally around the embryo with a corresponding decrease in volume of central endosperm with thick cell walls. In addition, distal endosperm cells adjacent to the depleted layer, containing reserve materials, were digested of contents following 21 days priming, and sometimes, following 7 days priming. A long priming duration resulted in degradation of pericarp tissues, as indicated visually and by a decline in pericarp volume. We hypothesize that priming duration of parsley primarily influences radicle growth and centrifugal digestion and utilization of central and distal endosperm, resulting in a larger depleted layer required for embryo volume increases. Secondary events influenced by priming duration include cotyledon growth and degradation of pericarp tissues.

Open access

Lisa Tang, Sukhdeep Singh, and Tripti Vashisth

In the past decade, FL citrus industry has been struck by Huanglongbing (HLB), a disease caused by the phloem-limited bacterium Candidatus Liberibacter asiaticus (CLas). Besides tree decline, HLB causes a sharp increase in mature fruit drop before harvest, leading to a substantial reduction in citrus production. The aim of the study was to provide insights in HLB-associated mature fruit drop. For HLB-affected ‘Valencia’ and ‘Hamlin’ sweet orange (Citrus sinensis), trees exhibiting severe symptoms (“severe trees”) had a significantly higher rate of mature fruit drop compared with mildly symptomatic ones (“mild trees”). Interestingly, dropped fruit were smaller than those still attached to tree branches regardless of the symptom levels of trees; overall, fruit of severe trees were smaller than mild trees. The result suggests a negative effect of HLB on fruit growth that may lead to a high incidence to drop subsequently at maturity. This possibility is further supported by the difference in immature fruit size as early as 2 months after bloom between severe and mild trees. Although HLB-triggered phloem plugging due to callose deposition in citrus leaves, which results in disrupted carbohydrate transport, has been documented in literature, the results of the histological analysis demonstrated no consistent pattern of callose deposition in the mature fruit pedicel in relation to the drop incidence. Additionally, sugar concentration in juice was not significantly different between dropped and attached fruit, providing evidence that carbohydrate shortage is not the case for dropped fruit and thus not the predominant cause of HLB-associated mature fruit drop. Notably, the midday water potential was significantly lower for severe than mild trees during the preharvest period (2 weeks before harvest of the current crop) in late March, which was also the second week after full bloom of return flowering. This suggests that altered tree water status due to HLB might limit fruit growth during the initial stage of fruit development (immediately after flowering) and/or increase the incidence of mature fruit abscission, leading to elevated preharvest fruit drop. Together, the results suggest that in the presence of HLB, strategies to increase fruit size and minimize additional stresses (especially drought) for the trees may improve mature fruit retention.

Open access

P. H. Bressan, Y.-J. Kim, S. E. Hyndman, P. M. Hasegawa, and R. A. Bressan

Abstract

The node position from which axillary buds were isolated from shoots of rose (Rosa hybrida L.) markedly affected their growth and development in culture. Those buds nearest to and furthest from the apex either failed to develop or took the longest time to develop in culture compared to those buds in the middle portion of the stem. Benzylamino purine (BA) at low concentrations (0.03 to 0.3 mg/liter) stimulated the development of the axillary buds of ‘Gold Glow’ but not of ‘Improved Blaze’. A photon flux density (400-700 nm) of 17μE m−2 s−1 for 12 to 24 hours daily was optimum for the stimulation of shoot multiplication, while 66 μE mm−2s−1 for 12 to 24 hr was optimum for root initiation and for subsequent successful transplantation to soil of tissue culture-derived plants. A constant temperature of 21°C resulted in the highest rate of shoot multiplication and root initiation. Plants which initiated roots at 16, 21, or 26° had the highest level of transplant survival. An alteration in the temperature of the 8-hr dark period from 21° did not increase shoot multiplication, although root initiation was enhanced by lowering the night temperature to 11 or 16°. Histological analysis indicated that shoot multiplication of rose shoots occurs through the growth and development of axillary buds. The development of axillary buds is apparently under the repressive influence of the shoot apex, because physical excision of the apex or application to the shoot apex of 2,3,5-triiodobenzoic acid (TIBA) facilitated axillary bud development. Root initiation was affected markedly by the length of time that cultures had been maintained on shoot multiplication medium prior to transfer to rooting medium. This effect may be attributable to the BA in the shoot multiplication medium which may have accumulated in the tissue. If the endogenous cytokinin level is too high, root initiation may be inhibited and if it is too low the shoot undergoes senescence before it becomes cytokinin-autonomous, which occurs after root initiation.

Open access

Li Xu, Fangyun Cheng, and Yuan Zhong

as explants ( Wen et al., 2020 ). Embryo culture is a tissue culture intervention usually adopted to overcome the postfertilization developmental barriers of the growing embryos; on the basis of the stage and histological origin of isolated embryos