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- Author or Editor: James Flore x
- Journal of the American Society for Horticultural Science x
Abstract
The influence of phyllotaxy and stage of leaf and fruit development on the initiation and direction of carbohydrate (CH2O) export from sour cherry (Prunus cerasus L.) leaves was investigated during two different seasons. One-year-old ‘Montmorency’ sour cherry trees on ‘Mahaleb’ rootstock were pruned to a single shoot, the seventh and 10th leaf (from the base) were pulsed with 14CO2, and labeled carbon products were located after 24 hr using autoradiography. In 1983, gross export (EG) from the seventh and 10th leaf was initiated when the area of the seventh leaf reached 8.5 cm2 (27% expansion) and when that of the 10th leaf reached 14 to 21 cm2 (48% to 72% expansion), respectively. EG was generally initiated later in 1985 than in 1983, for the seventh leaf later than 26 cm2 (47% expansion) and for the 10th leaf at 36 cm2 (78% expansion). Leaf size was greater at full expansion in 1985 than in 1983. On defoliated shoots, the 10th leaf (54 ± 16 cm2 full expansion) started export between 24 and 28 cm2 (44% to 52% expansion), whereas control leaves on nondefoliated shoots started export at 36 cm2 (78% expansion). We suggest that, after a leaf has developed the potential for phloem loading, the onset of CH2O export is a function of the CH2O availability in the plant at the time of leaf expansion. Translocation paths followed closely the orthostichy of the exporting leaf. Fruit effects on the direction of translocation were studied in 2-year-old trees. During stages I and III of fruit development, leaves closest to the base showed basipetal translocation only. All leaves during stage II and leaves distal to the midpoint of the shoot during stages I and III showed bidirectional translocation to the shoot apex and the fruits.
Abstract
Highbush (Vaccinium corymbosum L. ‘Bluecrop’) and rabbiteye (V. ashei Reade ‘Woodard’) blueberry plants were flooded in the greenhouse to determine how transpiration, stomatal conductance to water and CO2, residual conductance, and C assimilation are affected during flooding and recovery. Carbon assimilation was measured using a portable CO2 analyzer and stomatal conductance using a steady-state porometer. Stomatal conductance and transpiration decreased significantly after 4 to 5 days of flooding, and responses were similar for highbush and rabbiteye blueberries. Carbon assimilation decreased for both species within 9 days and became negative in 11 to 19 days due to decreased photosynthesis, stomatal conductance to CO2, and high leaf temperatures, which increased respiration. Recovery after 24 days of flooding to preflood stomatal conductance values required 18 days for ‘Woodard’ and more than 18 days for ‘Bluecrop’. In laboratory experiments flooded plants were less responsive to changes in ambient CO2 and vapor pressure deficits than unflooded plants, and flooding durations of greater than 9 days significantly decreased residual conductance of the leaves.
Apple seedlings (Malus domestica Borkh.) were grown under ambient (370), 700, and 1400 μmol·mol-1 CO2 regimes and artificially damaged by removal of leaf area (0%, 15%, and 30%). Increased CO2 concentration had a highly significant effect on the concentrations of sucrose, sorbitol and phloridzin, however there were no significant interactions between CO2 concentration and leaf damage. As CO2 concentration increased there was an increase in levels of sucrose and phloridzin, whereas sorbitol concentration decreased. These findings are discussed in relation to the carbon nutrient balance hypothesis as well as other hypotheses regarding the production of plant primary and secondary compounds in response to elevated levels of CO2 and mechanical damage and/or herbivory.
`Imperial Gala' apple trees (Malus ×domestica Borkh.) on M.9 EMLA, MM.111, and Mark rootstocks were subjected to two drought-stress and recovery periods in a rainshelter. Water relations, gas-exchange parameters per unit leaf area and per tree, chlorophyll fluorescence, and leaf abscisic acid content were determined during each stress and recovery period. Whole-plant calculated gas exchange best indicated plant response to drought stress, with consistent reductions in CO2 assimilation, transpiration, and leaf conductance. Variable and maximal chlorophyll fluorescence and fluorescence quenching were not as sensitive to stress. Other fluorescence parameters showed little difference. The most consistent decreases due to stress for gas exchange per square meter were in transpiration and leaf conductance, with few differences in CO2 assimilation and fewer for mesophyll conductance, internal CO2 concentration, and water-use efficiency. Leaf water potential was consistently lower during drought stress and returned to control values upon irrigation. Leaf abscisic acid content was higher for drought-stressed trees on M.9 EMLA than control trees during the stress periods but inconsistently different for the other rootstock treatments. Trees on M.9 EMLA were least affected by drought stress, MM.111 was intermediate, and Mark was the most sensitive; these results are consistent with the growth data.
`Imperial Gala' apple (Malus domestica Borkh.) trees, trained to two shoots, on M.9 EMLA, MM.111, and Mark rootstocks were subjected to two drought-stress and recovery periods in a rainshelter. Leaf growth rate, leaf area, leaf emergence, shoot length, and trunk cross-sectional area were measured during each stress and recovery period. Leaf growth rate was reduced during both stress periods but most consistently during the second drought stress. Length of the less-vigorous shoot was reduced most consistently due to drought stress but did not recover upon irrigation. Leaf emergence and trunk cross-sectional area increment were inconsistent in response to stress. Tree growth was reduced by drought stress to the greatest extent for trees on Mark, with MM.111 intermediate and M.9 EMLA least affected. At termination, the plants were separated into roots, current-season shoot growth, previous-season shoot growth, and rootstock, and dry weights were measured. Dry weights confirmed the growth measurements taken during the experiment with a 16%, 27%, and 34% reduction in total plant dry weight for drought-stressed trees on M.9 EMLA, MM.111, and Mark, respectively, compared to corresponding controls. It was concluded that Mark was the most sensitive of the three rootstocks followed by MM.111; M.9 EMLA was the most drought resistant.
Cucumber plants were cultured in a greenhouse and subjected to either well-watered or water deficit conditions that reduced leaf water potential to-0.6 MPa. Leaf gas exchange measurements were conducted using an open gas exchange system. Carbon dioxide assimilation (A) attained saturation at a photon flux density (PFD) of 1000 μmol·m-2·s-1 (400-700 nm). There were no significant differences in A at ambient temperatures between 16 and 34C. Water use efficiency decreased rapidly with increasing vapor-pressure deficits to 2.5 kPa. Water stressed plants had lower stomata1 conductances and CO2 assimilation rates. The decrease in A was only partially due to stomata1 closure. The A vs. intercellular CO (Ci) relationship for stressed leaves revealed a change in the CO, compensation point, and that nonstomatal factors were contributing to the decrease in A in stressed plants. Thus, feedback inhibition of A may have occurred through photoassimilate accumulation. The concentrations of sucrose and raffinose were higher, and the concentration of stachyose was lower in leaves of stressed than of well-watered plants.
Abstract
Changes in surface characteristics of the adaxial and abaxial cuticular membranes of expanding ‘Red-haven’ peach [Prunus persica (L.) Batsch] leaves were followed and related to wettability and to retention and penetration of foliar-applied compounds. Epicuticular wax deposition increased with leaf development until full expansion, the maximum being 50 to 65 μg cm−2. Although wax fine-structure was not prominent on expanding leaves, localized areas of crystalline wax occurred on both surfaces of fully expanded leaves. The 2 surfaces differed markedly in the composition of the epicuticular wax. Although triterpenoid acids, alkanes and primary alcohols were present on both surfaces, sterols and esters were predominant on the adaxial surface. Marked changes in composition occurred with leaf age. The contact angles formed by aqueous droplets on the adaxial surface increased with leaf development and attained the highest value only after full leaf expansion; on the abaxial surface the contact angle increased sharply and approached a maximum at 70 to 80% full expansion. Retention of aqueous solutions decreased with leaf expansion. Permeability of the cuticular membrane, as indexed by transpirational loss and penetration of 14C-NAA (naphthaleneacetic acid), decreased progressively with increasing leaf age. These findings are discussed in relation to spray application and penetration of foliar-applied chemicals.