James A. Flore

Gas Exchange and Carbon Partitioning in the Leaves of Celery (Apium graveolens L.) at Various Levels of Root Zone Salinity.

Both mannitol and sucrose (Suc) are primary photosynthetic products in celery (Apium graveolens L.). In other biological systems mannitol has been shown to serve as a compatible solute or osmoprotectant involved in stress tolerance. Although mannitol, like Suc, is translocated and serves as a reserve carbohydrate in celery, its role in stress tolerance has yet to be resolved. Mature celery plants exposed to low (25 mM NaCl), intermediate (100 mM NaCl), and high (300 mM NaCl) salinities displayed substantial salt tolerance. Shoot fresh weight was increased at low NaCl concentrations when compared with controls, and growth continued, although at slower rates, even after prolonged exposure to high salinities. Gas-exchange analyses showed that low NaCl levels had little or no effect on photosynthetic carbon assimilation (A), but at intermediate levels decreases in stomatal conductance limited A, and at the highest NaCl levels carboxylation capacity (as measured by analyses of the CO2 assimilation response to changing internal CO2 partial pressures) and electron transport (as indicated by fluorescence measurements) were the apparent prevailing limits to A. Increasing salinities up to 300 mM, however, increased mannitol accumulation and decreased Suc and starch pools in leaf tissues, e.g. the ratio of mannitol to Suc increased almost 10-fold. These changes were due in part to shifts in photosynthetic carbon partitioning (as measured by 14C labeling) from Suc into mannitol. Salt treatments increased the activity of mannose-6-phosphate reductase (M6PR), a key enzyme in mannitol biosynthesis, 6-fold in young leaves and 2-fold in fully expanded, mature leaves, but increases in M6PR protein were not apparent in the older leaves. Mannitol biosynthetic capacity (as measured by labeling rates) was maintained despite salt treatment, and relative partitioning into mannitol consequently increased despite decreased photosynthetic capacity. The results support a suggested role for mannitol accumulation in adaptation to and tolerance of salinity stress.

Ontogenetic variations in the composition of peach leaf wax

Abstract The composition of the epicuticular waxes from the adaxial and abaxial surfaces of peach leaves varies considerably during one seasons growth. Triterpenoid acids are major components 84–95% of the waxes from the youngest leaves but the proportions of these constituents decrease as the leaves expand. The waxes from the abaxial surfaces of fully expanded leaves consist primarily of hydrocarbons (C 22–C34 ) and triterpenoid acids, whereas the adaxial surface waxes also contain large proportions of primary alcohols (C 26 -C 34 ) and esters (C 42 -C 52 ). The latter include sitosteryl esters of hexacosanoic, octacosanoic and eicosanoic acids. Variations were also noted between fully expanded leaves of different ages, the abaxial surface waxes of the oldest leaves containing the highest proportions of hydrocarbons, whilst the wax from the adaxial surface of the corresponding leaves contained the largest amounts of esters, sitosterol and hydrocarbons.

The influence of micropropagation on yield components, dry matter partitioning and gas exchange characteristics of strawberry

Abstract Asexual progeny of micropropagated (MP) plants of the cultivars ‘Earliglow’ and ‘Redchief’ had higher plant densities and yields than conventionally propagated (CP) plants in matted rows. MP plants partitioned 9–10% less of their total dry matter to leaf tissue. Micropropagated ‘Redchief’ increased its allocation to crowns and flower trusses; ‘Earliglow’ to fruit. Leaf area crown −1 was reduced in MP ‘Earliglow’ (49%) and ‘Redchief’ (55%), and yield crown −1 was lower (32%) in MP ‘Redchief’, but not ‘Earliglow’. Net photosynthetic rate (mg CO 2 dm −2 h −1 or μg CO 2 g −1 dry wt. h −1 was greater in MP ‘Earliglow’ but not in ‘Redchief’. Stomatal conductance was higher in MP ‘Earliglow’, while mesophyll conductance was unchanged in both cultivars. MP plants of both cultivars had more stable PN rates across leaf densities than CP ones.

Effects of root-zone temperature on nitrogen accumulation by non-bearing apple trees

SummaryNon-bearing, potted, apple plants were subjected to root temperature of 8.6.1(LRT) or 23.6.18C (HRT) and irrigated with 100 ml of water containing 20 mg of N as NH4NO3, in which both ammonium and nitrate-N fractions were enriched in 15N (10 atom%). The root system of each plant was pressurized (325 kPa) at day 1, 2, 4, and 8 after15 N application to evaluate the transport of nitrogen derived from fertilizer (NDFF) through the xylem. This technique was used to investigate N absorption. LRT reduced the rate of N uptake the day after 15N application relative to HRT. Two, 4 and 8.d after fertilization, the rate of exudation and consequently the uptake rate was similar for LRT and HRT. The total amount of N removed by plants after 8.d was not affected by root treatments. Carbon dioxide assimilation, transpiration rate and stomatal conductance were lower for trees subjected to LRT during the time course of the experiment. We suggest that the delay in N absorption was related mostly to the lower activity ...

Annual additions of potassium to the soil increased apple yield in brazil

Potassium (K) is a very important nutrient for apples (Malus domestica) because it affects fruit quality and storage as well as yield. The amount of K to be applied varies with many plant and soil parameters, including cultivar, soil type, crop load, and climate. This study was carried out to assess the effect of long-term annual soil additions of K on fruit yield of a “Fuji” orchard grown in an Oxisol (Hapludox) previously well fertilized, under subtropical climate, in Southern Brazil. The trees (1234/ha), grafted on MM 106 rootstock, were planted in 1987. Potassium chloride was added annually to the soil surface, at rates of 0, 37, 75, 150, and 300 kg ha−1 of K2O. Addition of K increased fruit yield in 4 of 6 years, even when soil exchangeable K was still high. Maximum annual productivity varied from 73 to 120 t ha−1. To obtain maximum yields 196 to 225 kg ha−1 of K2O were required, but only about 70 kg−1 ha−1 year−1 of K2O was required to maintain the initial K value in the plow layer. Addition of K increased the concentration of K+ in the soil, leaves and fruits, reduced calcium (Ca) concentration in leaves and fruits, but had no effect on fruit quality and storability. Thus, application of K to “Fuji” orchards in Southern Brazil can maintain soil levels higher than those actually recommended for annual crops, without reducing fruit quality or storage life. *This study was economically sponsored by Agropecuaria Schio Ltda., Vacaria, RS, Brazil. ††Researcher of CNPq.

Gas exchange properties of strawberry species and their hybrids

Clones of Fragaria chiloensis had significantly higher rates of net CO2 assimilation (A), leaf conductance to water vapor (g1), residual conductance to CO2 (gr) and water use efficiency (WUE) than F. × ananassa. There was a significant correlation (P < 0.05) between A and percentage of recently derived F. chiloensis genes among several breeding populations.

Effects of multiple applications of methyl jasmonate on fruit ripening, leaf gas exchange and vegetative growth in fruit trees

Summary Multiple applications of methyl jasmonate (Me-J), at 10.mM, enhanced the rate of fruit ripening in peach ‘Redhaven’. The effect of Me-J on red colour development and fruit firmness was most pronounced in fruit treated six times with Me-J. Lower concentrations of Me-J had no effect of fruit colour. Me-J, at 10.mM, significantly reduced stomatal conductance, photosynthetic rate and transpiration rate of crabapple leaves, but had no effect on these parameters in peach leaves. The short-term inhibitory effects of Me-J on leaf gas exchange in crabapple persisted for up to 24 h. Fourteen applications of Me-J over a period of 28 days resulted in a 60% decrease in the concentration of chlorophyll in leaves. These Me-J applications also reduced the length of new branches, leaf number and leaf fresh weight by 65%, 31% and 47%, respectively. In peach, Me-J induced some leaf chlorosis and early leaf senescence within two weeks of the treatments which resulted in significant reductions in shoot length.

Variation in leaf photosynthetic rates and yield in strawberries

SummaryVariability in CO2 assimilation rate (A) was measured in seven cultivars on five dates and three cultural systems using the stability analysis of Finlay and Wilkinson. The regression coefficient (b) of net photosynthetic rates was significantly correlated (r = 0.75) with yield, even though mean A was not. The highest yielding cultivars had b>l, suggesting that they did better than lower yielding genotypes in environments favouring high A. Most cultivars had significantly higher A on double hills than in ribbons or matted rows, and were photo- synthetically more active when producing fruit and runners than at anthesis.

Photosynthetic Performance of Pinot gris (Vitis vinifera L.) Grapevine Leaves in Response to Potato Leafhopper (Empoasca fabae Harris) Infestation

Potato leafhopper (Empoasca fabae Harris) is a polyphagous insect pest that feeds on Vitis vinifera L. grapevines in North America. In sensitive grape cultivars such as Pinot gris, feeding symptoms include leaf yellowing, leaf cupping, and stunted vine growth. Two greenhouse experiments were conducted to determine how photosynthesis and other physiological processes are affected by E. fabae infestation. In Experiment I, Pinot gris leaves at four different positions along shoots were infested with either 0, 1, 2, 4, or 8 E. fabae nymphs for 43 hr to determine how the relationship between infestation level and leaf position affects leaf photosynthesis and whether or not damage thresholds exist for the photosynthetic response. Empoasca fabae infestation was inversely proportional to carbon assimilation (A), transpiration (E), and stomatal conductance (Gs) and directly proportional to internal CO2 concentration (Ci). There was a positive correlation between A and Gs, while A and Ci were negatively correlated, indicating that reductions in A were due to both stomatal and nonstomatal limitations. Damage thresholds, defined as the number of insects necessary to cause damage to the plant, were calculated for A, E, Gs, and Ci at most leaf positions. In Experiment II, response curves were generated for infested and uninfested regions of the same leaves to determine how light and CO2 utilization were affected by E. fabae infestation. Declining A in response to E. fabae infestation was due to a decreased capacity of leaf tissues to utilize light and CO2. Reductions in A were correlated with decreases in Gs and increases in Ci, indicating that stomatal and nonstomatal limitations were relevant, with evidence of photosynthetic compensation in the postinfestation period. These results indicate that E. fabae infestation causes injury through rapid effects on the capacity of leaves to produce photosynthate through effects on internal tissues and on stomata. These effects might be transient at low infestation levels, but leaf tissue can be compromised at higher infestation levels, leading to irreversible damage.

Evaluation of nitrate-nitrogen leaching from lysimeter-grown bearing apple trees

A 2-year investigation was conducted on eight replicate plots located 30 miles east of Lake Michigan on sand to sandy-clay-loam soil, using 1.8-m-deep lysimeters (4.8 m3 of volume), consisting of an undisturbed monolith excavated from the soil and containing a bearing (2- to 3-year-old) apple tree each. The aims of this research were to study the leaching rate and migration time of nitrate-N (NO3−-N) through the soil profile and to assess the suitability of soil suction tube (SST) water samples to predict the NO3−-N leaching rate. The NO3−-N concentration in the water collected by the lysimeters ranged from less than 10 mg L−1 (in late summer) to more than 40 mg L−1 (in winter). We calculated that NO3−-N lost via leaching in a year amounts up to 141 kg ha−1, with the most potential for groundwater pollution occurring during the cold and wet season. The application of labeled N ammonium nitrate as fertilizer increased the concentration of NO3−-N in the solution collected by SST. Labeled N was found at the bottom of lysimeters 3 months after its application, leaching through the soil profile at a speed of 2 cm day−1, so that the NO3−-N concentration of SST was correlated significantly with NO3−-N concentration of lysimeters only when the time of movement was considered. The application of fertilizer did not increase the amount of NO3−-N collected by lysimeters, meaning that the NO3−-N leaching rate is mostly the result of the breakdown of soil organic matter.