A whole-plant, open, gas-exchange system for measuring net photosynthesis of potted woody plants.

Chambers were constructed to measure gas exchange of entire potted grapevines (Vitis vinifera L.). The plant enclosures were constructed from Mylar film, which is nearly transparent to photosynthetically active radiation. Maintaining a slight, positive, internal pressure allowed the Mylar chambers to inflate like balloons and required no other means of support. The whole-plant, gas-exchange chamber design and construction were simple and inexpensive. They were assembled easily, equilibrated quickly, and did not require cooling. They allowed for the measurement of any plants in a relatively short period. This system would enable the researcher to make replicated comparisons of treatment influences on whole-plant CO2 assimilation throughout the growing season. While CO2 measurement was the focus of this project, it would be possible to measure whole-plant transpiration with this system.

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.

Short-Term Flooding Effects on Gas Exchange and Quantum Yield of Rabbiteye Blueberry (Vaccinium ashei Reade).

Roots of 1.5-year-old ;Woodard' rabbiteye blueberry plants (Vaccinium ashei Reade) were flooded in containers or maintained at container capacity over a 5-day period. Carbon assimilation, and stomatal and residual conductances were monitored on one fully expanded shoot/plant using an open flow gas analysis system. Quantum yield was calculated from light response curves. Carbon assimilation and quantum yield of flooded plants decreased to 64 and 41% of control values, respectively, after 1 day of flooding and continued decreasing to 38 and 27% after 4 days. Stomatal and residual conductances to CO(2) also decreased after 1 day of flooding compared with those of unflooded plants with residual conductance severely limiting carbon assimilation after 4 days of flooding. Stomatal opening occurred in 75 to 90 minutes and rate of opening was unaffected by flooding.

A BASIC computer program for calculation of photosynthesis, stomatal conductance, and related parameters in an open gas exchange system.

Computer programs written in BASICA (IBM'S VERSION OF BASIC) language were developed for the calculation of the gas exchange parameters of CO2 assimilation, leaf conductance, stomatal conductance, residual conductance, intercellular CO2 concentration, transpiration, water use efficiency and transpiration ratio in an open system. Formulas are discussed in both an algebraic and in a BASIC computer program form. Calculations based on mole fractions of CO2 and water vapor are explained and both molar and mass fluxes are included in the program output to facilitate comparisons with data from the literature. Corrections are made in the program to account for under-estimation of CO2 assimilation due to the increase in flow rates out of sample chambers caused by simultaneous transpiration. A sample output is included to illustrate the formatting capability of the program.

Net photosynthetic rate of sour cherry (Prunus cerasus L. 'Montmorency') during the growing season with particular reference to fruiting.

Diurnal and seasonal net photosynthetic rates (Pn) of sour cherry were determined. Leaf Pn was not significantly affected by shoot excision. Under constant environmental conditions (PFD, 1200 µmol m(-2) s(-1); temp. 25; relative humidity, 80-90%) there was no significant diurnal fluctuation in Pn for individual leaves. However, there was a pronounced fluctuation in Pn for whole trees measured under constant temperature but natural variation in sunlight from sunrise to sunset. Maximum Pn occurred before solar noon, remained constant for 1-2 hr, then declined. Photosynthetic rate of recently expanded leaves fluctuated through out the season but, in general, was greatest in the spring as leaves expanded, reached a peak, remained stable for several weeks, then gradually declined. The Pn of leaves on terminal shoots was not significantly different from the Pn of leaves on spurs of the same physiological age. The presence of fruit did not have a consistent effect on the Pn of sour cherry leaves.

Net photosynthetic rate of sour cherry (Prunus cerasus L. 'Montmorency') during the growing season with particular reference to fruiting.

Diurnal and seasonal net photosynthetic rates (Pn) of sour cherry were determined. Leaf Pn was not significantly affected by shoot excision. Under constant environmental conditions (PFD, 1200 µmol m(-2)s(-1); temp. 25; relative humidity, 80-90%) there was no significant diurnal fluctuation in Pn for individual leaves. However, there was a pronounced fluctuation in Pn for whole trees measured under constant temperature but natural variation in sunlight from sunrise to sunset. Maximum Pn occurred before solar noon, remained constant for 1-2 hr, then declined. Photosynthetic rate of recently expanded leaves fluctuated through out the season but, in general, was greatest in the spring as leaves expanded, reached a peak, remained stable for several weeks, then gradually declined. The Pn of leaves on terminal shoots was not significantly different from the Pn of leaves on spurs of the same physiological age. The presence of fruit did not have a consistent effect on the Pn of sour cherry leaves.

Mechanism of Indole-3-acetic Acid Conjugation: No Induction by Ethylene.

Formation of indole-3-acetic acid-aspartate in detached primary leaves of cowpea (Vigna sinensis Endl.) floating on (14)C-indole-3-acetic acid (3 muc; 3.15 mum, phosphate-citrate buffer, pH 4.75), almost doubled when leaves were pretreated with 31.5 mum(12)C-indole-3-acetic acid for 17 hr and then transferred to (14)C-indole-3-acetic acid for 4 hours as compared with leaves preincubated in buffer only. When leaves were preincubated with ethylene (11.0 and 104 mul/l) instead of (12)C-indole-3-acetic acid, no induction of indole-3-acetylaspartic acid formation was observed, and the rate of indole-3-acetylaspartic acid formation decreased as compared with control leaves. Rhizobitoxine (1.87 mum) inhibited indole-3-acetic acid-induced ethylene production but did not prevent the formation of indole-3-acetylaspartic acid. In view of the similarity of these results and those previously obtained with alpha-naphthaleneacetic acid, it is concluded that ethylene has no role in the auxin-induced indole-3-acetylaspartic acid formation in cowpea leaves.