Measurements of (a) photosynthesis rate (<i>A</i>), (b) stomatal conductance (<i>g</i>_s), (c) mesophyll conductance (<i>g</i>_m), and (d) intrinsic transpiration efficiency (<i>A</i>/<i>g</i>_s) in control and water-stressed leaves of the seven <i>Oryza sativa</i> genotypes.

<p>The measurements were made on the flag leaf in saturating PPFD (1400 µmol m⁻²s⁻¹), with relative humidity ranging between 45–55%, and a leaf temperature of 30°C. Data are means of 4 to 7 plants per treatment. Error bars as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0109054#pone-0109054-g001" target="_blank">Figure 1</a>. Different letters denote significant differences among means derived using a factorial ANOVA and Tukey <i>post-hoc</i> test.</p

Interaction of yield and <i>A</i> with transpiration efficiency (<i>A</i>/<i>g</i>_s) and the ratio of <i>g</i>_m to <i>g</i>_s in well-watered (open symbols) and drought conditions (closed symbols): a) relationship between yield and <i>A</i>/<i>g</i>_s under full (linear regression: R² = 0.0595; <i>F</i>_1,4 = 0.253; <i>P</i> = 0.641) and water-stressed (linear regression: R² = 0.434; <i>F</i>_1,4 = 3.072; <i>P</i> = 0.155) conditions; b) relationship between harvest index (<i>HI</i>) and <i>A</i>/<i>g</i>_s under full (linear regression: R² = 0.205; <i>F</i>_1,4 = 1.032; <i>P</i> = 0.367) and water-stressed (linear regression: R² = 0.185; <i>F</i>_1,4 = 0.909; <i>P</i> = 0.394) conditions; c) relationship between yield and <i>g</i>_m:<i>g</i>_s (linear regression: R² = 0.456; <i>F</i>_1,10 = 8.379; <i>P</i> = 0.

<p>Error bars as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0109054#pone-0109054-g001" target="_blank">Figure 1</a>. Numbers next to data points indicate <i>Oryza sativa</i> variety as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0109054#pone-0109054-g001" target="_blank">Figure 1</a>.</p

Photosynthetic Diffusional Constraints Affect Yield in Drought Stressed Rice Cultivars during Flowering

<div><p>Global production of rice (<i>Oryza sativa</i>) grain is limited by water availability and the low ‘leaf-level’ photosynthetic capacity of many cultivars. <i>Oryza sativa</i> is extremely susceptible to water-deficits; therefore, predicted increases in the frequency and duration of drought events, combined with future rises in global temperatures and food demand, necessitate the development of more productive and drought tolerant cultivars. We investigated the underlying physiological, isotopic and morphological responses to water-deficit in seven common varieties of <i>O. sativa</i>, subjected to prolonged drought of varying intensities, for phenotyping purposes in open field conditions. Significant variation was observed in leaf-level photosynthesis rates (<i>A</i>) under both water treatments. Yield and <i>A</i> were influenced by the conductance of the mesophyll layer to CO₂ (<i>g</i>_m) and not by stomatal conductance (<i>g</i>_s). Mesophyll conductance declined during drought to differing extents among the cultivars; those varieties that maintained <i>g</i>_m during water-deficit sustained <i>A</i> and yield to a greater extent. However, the variety with the highest <i>g</i>_m and yield under well-watered conditions (IR55419-04) was distinct from the most effective cultivar under drought (Vandana). Mesophyll conductance most effectively characterises the photosynthetic capacity and yield of <i>O. sativa</i> cultivars under both well-watered and water-deficit conditions; however, the desired attributes of high <i>g</i>_m during optimal growth conditions and the capacity for <i>g</i>_m to remain constant during water-deficit may be mutually exclusive. Nonetheless, future genetic and physiological studies aimed at enhancing <i>O. sativa</i> yield and drought stress tolerance should investigate the biochemistry and morphology of the interface between the sub-stomatal pore and mesophyll layer.</p></div

Carbon isotope discrimination (‰) of the flag leaf pellet (bulk) and soluble sugars of seven rice cultivars grown under drought and well-watered conditions in ‰.

<p>Values indicate the mean of six plants; ± indicates the standard error of mean; different letters indicate significant differences (P≤0.05) among means according to an ANOVA.</p><p>Carbon isotope discrimination (‰) of the flag leaf pellet (bulk) and soluble sugars of seven rice cultivars grown under drought and well-watered conditions in ‰.</p

Changes in yield and photosynthesis in relation to modification of diffusive resistances to CO₂ uptake following water-stress.

<p>Those varieties that experienced smaller reductions in parameters were more tolerant of drought. a) relationship between Δyield and Δ<i>g</i>_s (linear regression: R² = 0.337; <i>F</i>_1,4 = 2.032; <i>P</i> = 0.227); b) relationship between Δyield and Δ<i>g</i>_m (linear regression: R² = 0.134; <i>F</i>_1,4 = 0.618; <i>P</i> = 0.476); c) relationship between Δyield and Δ<i>g</i>_tot (linear regression: R² = 0.0818; <i>F</i>_1,4 = 0.356; <i>P</i> = 0.583); d) relationship between Δ<i>A</i> and Δ<i>g</i>_s (linear regression: R² = 0.0003; <i>F</i>_1,4 = 0.00106; <i>P</i> = 0.976); e) relationship between Δ<i>A</i> and Δ<i>g</i>_m (linear regression: R² = 0.742; <i>F</i>_1,4 = 11.527; <i>P</i> = 0.0274); f) relationship between Δ<i>A</i> and Δ<i>g</i>_tot (linear regression: R² = 0.715; <i>F</i>_1,4 = 10.042; <i>P</i> = 0.0339), and; g) relationship between Δyield and Δ<i>A</i> (linear regression: R² = 0.427; <i>F</i>_1,4 = 2.979; <i>P</i> = 0.159). Error bars as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0109054#pone-0109054-g001" target="_blank">Figure 1</a>. Numbers next to data points indicate <i>Oryza sativa</i> variety as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0109054#pone-0109054-g001" target="_blank">Figure 1</a>.</p

Interaction of diffusive conductance parameters to CO₂ uptake with yield and photosynthesis (<i>A</i>) under well-watered (open symbols) and drought conditions (closed symbols): a) relationship between yield and stomatal conductance (<i>g</i>_s) (linear regression: R² = 0.696; <i>F</i>_1,10 = 22.900; <i>P</i> = 0.000740); b) relationship between <i>A</i> and <i>g</i>_s (linear regression: R² = 0.873; <i>F</i>_1,11 = 75.721; <i>P</i> = 2.911×10^–6); c) relationship between yield and mesophyll conductance (<i>g</i>_m) (linear regression: R² = 0.850; <i>F</i>_1,10 = 56.611; <i>P</i> = 2.911×10^–5); d) relationship between <i>A</i> and <i>g</i>_m (linear regression: R² = 0.952; <i>F</i>_1,11 = 217.071; <i>P</i> = 1.376×10^–8); e) relationship between yield and total conductance (<i>g</i>_tot) (linear regression: R<sup

<p>Error bars as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0109054#pone-0109054-g001" target="_blank">Figure 1</a>. Numbers next to data points indicate <i>Oryza sativa</i> variety as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0109054#pone-0109054-g001" target="_blank">Figure 1</a>.</p

Measurements of (a) the intercellular [CO₂] (<i>C</i>_i) to the ambient [CO₂] (<i>C</i>_a) ratio (<i>C</i>_i/<i>C</i>_a), and (b) the chloroplastic [CO₂] (<i>C</i>_c) to the ambient [CO₂] ratio (<i>C</i>_c/<i>C</i>_a) in control and water-stressed leaves of the seven <i>Oryza sativa</i> genotypes.

<p>The measurements were made on the flag leaf in saturating PPFD (1400 µmol m⁻²s⁻¹), with relative humidity ranging between 45–55%, and a leaf temperature of 30°C. Data are means of 4 to 7 plants per treatment. Error bars as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0109054#pone-0109054-g001" target="_blank">Figure 1</a>. Different letters denote significant differences among means derived using a factorial ANOVA and Tukey <i>post-hoc</i> test.</p

Comparison between the estimates of mesophyll conductance of CO₂ (<i>g</i>_m) obtained by applying two independent methods: the variable <i>J</i> method and the ‘δ13C of recently synthesised sugars’ method (linear regression: R² = 0.932; <i>F</i>_1,9 = 122.750; <i>P</i> = 1.515×10⁻⁶).

<p>Each data point represents the average value of three observations based upon the Δ13C of recently synthesised sugars and six to fourteen gas-exchange measurements utilising the variable J method. Error bars as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0109054#pone-0109054-g001" target="_blank">Figure 1</a>. The regression line excludes the two data points on the right of the graph (IR64 and PS80) with anomalously high <i>g</i>_m derived from the δ13C of recently synthesised sugars. Numbers next to data points indicate <i>Oryza sativa</i> variety as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0109054#pone-0109054-g001" target="_blank">Figure 1</a>.</p

Transcriptome Profiling of Leaf Elongation Zone under Drought in Contrasting Rice Cultivars

<div><p>Inhibition of leaf elongation and expansion is one of the earliest responses of rice to water deficit. Despite this sensitivity, a great deal of genetic variation exists in the extant of leaf elongation rate (LER) reduction in response to declining soil moisture. We analyzed global gene expression in the leaf elongation zone under drought in two rice cultivars with disparate LER sensitivities to water stress. We found little overlap in gene regulation between the two varieties under moderate drought; however, the transcriptional response to severe drought was more conserved. In response to moderate drought, we found several genes related to secondary cell wall deposition that were down regulated in Moroberekan, an LER tolerant variety, but up-regulated in LER sensitive variety IR64.</p> </div

Relative leaf elongation under soil drying.

<p>Bars represent +/- SE.</p