`Braeburn' apple trees were treated with GA3 or GA7 at either 100, 200, or 400 mg·L-1, 2 years after being grafted onto 4-year-old `Royal Gala'/MM.106 trees in order to evaluate their effects on flower bud formation. Inhibition of flowering was observed on 1-year wood only and not on spurs in response to GA treatments applied later than 6 weeks after bloom. GA7 was a more potent inhibitor of flowering than GA3. These results indicate that GA treatments may provide a useful technology for the selective removal of flowers from 1-year wood in apple and may also provide a useful tool for overcoming biennial bearing in apple by inhibiting flower bud formation when applied in the light-cropping year of the biennial cycle.
Cold stress is an important factor that limits grape (Vitis sp.) production around the world. The high expression of osmotically responsive genes 1 (HOS1) protein acts as a repressor of cold-responsive genes in plants. To increase understanding of mechanism regulating cold tolerance in grape, we isolated and characterized a novel HOS1 gene, designated VvHOS1 from ‘Muscat Hamburg’ grapevine (Vitis vinifera). Real-time polymerase chain reaction (PCR) analysis revealed that the expression of VvHOS1 could be induced by the application of exogenous abscisic acid and various abiotic environmental conditions such as low temperature, drought, and salinity. Moreover, VvHOS1 expression could also be induced by cold plus drought conditions (4 °C, 10% polyethylene glycol 6000). In addition, overexpression of VvHOS1 in arabidopsis (Arabidopsis thaliana) decreased the plants’ tolerance to cold, drought, and salt as well as negatively regulated the expression level of two stress-responsive genes, AtRD29A and AtCOR47. The results obtained in this study should help us to elucidate the function of VvHOS1 and understand the cold-responsive pathway in grapevine.
The responses of photosynthesis, chlorophyll fluorescence, and de-epoxidation state of the xanthophyll cycle pigments (DEPS) of micropropagated apple trees (Malus ×domestica) were investigated under whole-root water stress (WRS) and half-root water stress (HRS) induced by polyethylene glycol 6000 to simulate whole and partial root zone drying. Compared with control plants without water stress, plants under WRS and HRS exhibited reduced leaf net photosynthetic rate (Pn) and stomatal conductance (gS) with a greater reduction in WRS than in HRS plants. However, intercellular CO2 concentration (Ci) increased under WRS as water stress was prolonged, signifying a non-stomatal limitation of Pn. Regarding HRS, decreased Pn was mainly the result of a stomatal limitation explained by a relatively low Ci. Changes in photosynthesis and chlorophyll parameters indicate that severe and slight damage occurred to the photosynthetic apparatus of WRS and HRS leaves, respectively, starting at Day 3 after initiating water stress. This damage was not evident on the donor side but was expressed as a reduced capacity of the acceptor side of the photosystem II reaction centers. To prevent damage from excess light, the DEPS of WRS leaf increased. Decreased gS could explain reduced water use under an irrigation strategy of partial root zone drying in fruit trees.
In ‘Beijing 24’ peach [Prunus persica (L.) Batch] trees, a series of source leaves with differing levels of end products were created by retaining fruit (“+fruit”), removing fruit (“−fruit”), or reducing the light period. To alter the light period, leaves were covered with a bag made of brown inner paper and outer silver paper, which was then removed at different times the next day. The highest level of end products were obtained by fruit removal, while reducing the light period resulted in a lower level than “+fruit.” Net photosynthetic rate (Pn) and stomatal conductance (gs) decreased, but leaf temperatures (Tleaf) increased, following an increase in end product levels in leaves. After the “−fruit” treatment, reduced Pn was correlated with lower gs, and Tleaf increase was concomitant with decreases in maximal quantum yield of photosystem II (Fv/Fm), actual photochemical efficiency of photosystem II (ΦPSII), and photochemical quenching, and with an increase in nonphotochemical quenching. However, there were no significant differences in chlorophyll fluorescence between “+fruit” and the two treatments reducing the light period. The ΦPSII decreased following an increase in foliar sorbitol level, and it linearly decreased as sucrose and starch increased. Although fruit removal resulted in a significant accumulation of sucrose, sorbitol, and starch in leaves throughout the day, the extractable activities of several important enzymes involved in carbohydrate leaf storage and translocation did not decrease. Therefore, instead of feedback regulation by the accumulation of end products in source leaves, a high Tleaf induced by decreased stomatal aperture may play a key role in regulation of photosynthesis by limiting the photochemical efficiency of the PSII reaction centers under high levels of the end products in peach leaves.
The most obvious effects of a low leaf:fruit (LF) ratio [two leaves for one cluster per shoot (LF2)] on grape (Vitis vinifera) berries are suppressed anthocyanin biosynthesis in the berry skin, decreased berry weight and soluble solids concentration, and increased titratable acidity. In this study, proteins isolated from berry skins grown under low and high LF ratio conditions, LF2 and LF12, respectively, were characterized by two-dimensional gel electrophoresis coupled to mass spectrometry. A survey of ≈600 to 700 spots from berry skin yielded 77 proteins with differential expression between LF12 and LF2 treatments. Of these, the 59 proteins that were identified consisted of 47 proteins that were down-regulated and 12 that were up-regulated under LF2 conditions compared with LF12 conditions. Most proteins involved in metabolism, energy, transcription, protein synthesis, binding function, signal transduction, and cell defense were down-regulated in LF2 berries, whereas two important enzymes of anthocyanin biosynthesis, chalcone synthase and dihydroflavonol reductase, were not detected. Only a few proteins (e.g., two heat shock proteins related to protein fate and nutrient reservoir storage protein) were found to be up-regulated in LF2 berries. This suggested that, with the exception of secondary metabolism, many proteomic events may have an effect on anthocyanin synthesis in the skins responding to LF.
Sorbitol is the primary photosynthate and translocated carbohydrate in apple (Malus ×domestica), and most of it is converted to fructose by sorbitol dehydrogenase (SDH) in sink tissues. We studied the expression of nine SDH genes, SDH activity, and sorbitol content of apple 1) in buds and floral tissues from dormancy to bloom, 2) in leaves and shoot tips of trees on two rootstocks, the moderately vigorous ‘Malling Merton 111’ (MM.111) and the dwarfing ‘Malling 9’ (M.9), and 3) in shoot tips in response to application of prohexadione-Ca to suppress shoot growth and defoliation and girdling (D/G) to deprive the shoot tip of sorbitol. In mature, orchard-grown trees, sorbitol was the main soluble carbohydrate in expressed xylem sap from dormancy to bloom at levels over 3- to 6-fold those of glucose and fructose, the other major sugars present. Sorbitol levels there increased from dormancy to its highest concentration at the half inch green stage and declined by bloom, while those of the other sugars increased. SDH activity per milligram of protein increased over 4-fold from dormancy to flowering. Three of the nine known SDH genes (SDH1, SDH2, and SDH3) were expressed in immature and mature leaves and all buds from dormancy to bloom, as well as in all floral organs, except that only SDH3 transcript was found in stamen tissue. Two genes, SDH6 and SDH9, were floral-tissue specific; SDH6 transcript was detected in all floral organs except stamens at full bloom, and SDH9 was only expressed in anthers with pollen. In buds and leaves of young, container-grown trees, SDH1 and SDH2 generally accounted for the majority of total SDH expression. There were generally no effects of rootstock on SDH expression, SDH activity, or sorbitol concentration in leaves, while apical shoot tips on M.9 rootstock exhibited greater SDH activity than those on MM.111 or lateral shoot tips on either rootstock, though SDH expression of apical and lateral shoot tips on M.9 was lower than on MM.111. Prohexadione-Ca reduced apical but not lateral shoot growth, increased apical but not lateral shoot tip sorbitol content, had no effect on SDH activity, and increased SDH1 expression of all shoot tips. D/G treatment reduced shoot growth, sorbitol content, and SDH activity, but increased SDH1 expression of apical shoot tips only and SDH2 expression of lateral shoot tips only. This work indicates that sorbitol and other sugars are abundantly available from dormancy to bloom, that SDH activity increased during this period, and that SDH expression is at least in part developmentally regulated within the individual floral and leaf tissues. In shoot tips and leaves of young trees, SDH transcript level was not correlated with sorbitol availability or SDH activity, suggesting that other factors have significant regulatory effects after SDH expression on SDH activity.
The genetic relationships among 96 peach and nectarine [Prunus persica (L.) Batsch.] genotypes and botanical varieties originating from different ecogeographical regions of China, Japan, North America, and South Korea were evaluated with 33 SSR markers screened from 108 published SSR markers developed for peach or sweet cherry (P. avium L.). The 33 SSRs detected polymorphisms among 96 genotypes and revealed a total of 283 alleles with an average of 8.6 alleles per locus. The polymorphism information content (PIC) value ranged from 0.40 (BPPCT041) to 0.98 (BPPCT009) with an average of 0.80. Unweighted pair group method average (UPGMA) cluster analysis based on Nei's genetic distances classified genotypes into six groups, corresponding to their ecogeographical origin. Group I consisted of northern Chinese and northwestern Chinese local cultivars, and was divided into two subgroups, white and yellow peaches. Group II contained mainly southern Chinese local, Japanese, and North American cultivars and can be divided into four subgroups: Japanese white, Chinese flat, North American yellow, and some Chinese local ornamental peach cultivars. Groups III, IV, and V were comprised of Chinese local ancient cultivars, and contained `Xinjiangdatianren' and `Renmiantao', Chinese dwarf cultivars, and `Fenshouxing', respectively. Group VI had only `Baishanbitao', a Chinese ornamental cultivar. Northern and northwestern Chinese local cultivars clustered together with a greater diversity than southern Chinese local cultivars, indicating that the northern and northwestern Chinese local cultivars are similar ecotypes, and southern Chinese local cultivars are a subset of the northern Chinese group. Moreover, the Japanese and North American genotypes had a close phylogenetic relationship with southern Chinese local cultivars. The taxonomic placement of P. ferganensis (Kost. et Kiab) Kov. et Kost. and the phylogenetic relationship of `Baishanbitao' with peaches are discussed.
Inter-simple sequence repeat (ISSR) markers were used to evaluate genetic similarity and interrelationship among 104 plum (Prunus L. spp.) and related accessions from the Chinese National Germplasm Repository for Plums and Apricots and the Tianshan Germplasm Repository for Wild Fruit Resources, including six plum species (Prunus salicina Lindl., Prunus simonii Carr., Prunus ussuriensis Kov. et Kost., Prunus domestica L., Prunus cerasifera Ehrh., and Prunus spinosa L.), two related species [apricot (Prunus armeniaca L.) and nanking cherry (Prunus tomentosa Thunb.)], eight putative hybrids between plum and apricot (plumcot), and six accessions of wild European plum (P. domestica). Out of the 42 ISSR primers, 12 were selected, which generated 103 markers in total, 99 of which were polymorphic. Possible accession-specific ISSR bands or patterns were also found. Some possible synonyms or homonyms were clarified or discussed, and closely related accessions such as bud mutants were discriminated. Based on the unweighted pair group method with arithmetic mean (UPGMA) analysis and principal coordinate analysis (PCoA) using the Jaccard coefficient, two different dendrograms were constructed—one including accessions grouped by species and one with all 104 accessions—and a two-dimensional plot was obtained. Three groups were formed in both dendrograms and PCoA plot: Group I including apricot (‘Yinxiangbai’) and plumcot types; Group II containing Asia-originated diploid species [e.g., P. cerasifera, P. ussuriensis, P. tomentosa, and Chinese plum-types (i.e., P. salicina and its hybrids)]; and Group III involving European-origin polyploid species (e.g., P. spinosa and P. domestica) and recently found wild European plum accessions in China. The dendrogram with accessions grouped by species implied that 1) plumcot types had closer relatedness with apricot than with plum; 2) P. simonii should be a variant of P. salicina while P. ussuriensis an independent species; 3) P. domestica was more closely related to P. spinosa than to P. cerasifera. Two accessions of European plum (‘89-7-3’ and ‘Wanhei’) were clustered into outgroups in the dendrogram with all 104 accessions, which could been grouped within Group III in the PCoA plot. The distribution of both European plum and Chinese plum-types across respective groups did not reflect the geographic origins. The present study also further confirmed that the wild plants found in Xinjiang of China were P. domestica.