Water Deficits and Environmental Factors Affect Photosynthesis in Leaves of Cucumber (Cucumis sativus)

Abstract

<jats:p>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 <jats:italic>(A)</jats:italic> attained saturation at a photon flux density (PFD) of 1000 μmol·m<jats:sup>-2</jats:sup>·s<jats:sup>-1</jats:sup> (400-700 nm). There were no significant differences in <jats:italic>A</jats:italic> 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 CO<jats:sub>2</jats:sub> assimilation rates. The decrease in <jats:italic>A</jats:italic> was only partially due to stomata1 closure. The <jats:italic>A</jats:italic> vs. intercellular CO (C<jats:sub>i</jats:sub>) relationship for stressed leaves revealed a change in the CO, compensation point, and that nonstomatal factors were contributing to the decrease in <jats:italic>A</jats:italic> in stressed plants. Thus, feedback inhibition of <jats:italic>A</jats:italic> 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.</jats:p>

Whole-plant Carbon Dioxide Exchange Responses of Angelonia angustifolia to Temperature and Irradiance

“…In contrast, Welander and Hellgren (1988) showed that increasing temperature from 18 to 24 °C decreased whole plant P net of geranium, but their data were collected at very low PPF levels (30 to 150 µmol·m -2 ·s -1 ). The decrease in P net at high temperatures may have been caused by several factors: a decrease in gross photosynthesis, an increase in photorespiration, an increase in respiration other than photorespiration, feedback inhibition of photosynthesis after a long period of light exposure, or stomatal closure in response to increasing vapor pressure deficit at higher temperatures (Janoudi et al, 1993;Jiao and Grodzinski, 1996;van Iersel and Lindstrom, 1999). It is important to realize that the optimal temperature for P net depends on the temperature at which plants are grown.…”

Drought Response of Three Ornamental Herbaceous Perennials

“…Sucrose becomes concentrated in leaves during drought due to reduced sucrose export from the leaves, which is thought to be due to reduced export of protons that are the cotransporters of sucrose in the phloem (Malek and Baker, 1978). In plants of other species, accumulation of phototsynthates in the leaves during drought (Ackerson, 1980;Azcon-Bieto, 1983) has acted as a feedback-inhibition mechanism (Janoudi et al, 1993) to A. Eupatorium rugosum had the most stable carbohydrate partitioning in the leaves compared to the other taxa, having only an increase in fructose content (Table 2). Glucose and sucrose contents in the leaves of treated R. triloba were greater than the content of the controls 4 DAFD (Table 2).…”

A test of the hydraulic limitation hypothesis in fast‐growingEucalyptus saligna

“…One possible mechanism consistent with these data is a reduced triose phosphate utilization (Harley & Sharkey 1991; Harley et al . 1992) in the 5 year trees, perhaps caused by the effect of a 0.8 MPa lower Ψ leaf on translocation and growth (Janoudi, Widders & Flore 1993; Hsiao 2000; Hsiao & Xu 2000). Differences in triose phosphate utilization could cause differences in diurnal photosynthesis in the 1 and 5 year trees, even though our assessments of photosynthetic capacity ( A max , V c,max , and foliar N) were similar.…”