S-stapfianus and E-curvula cv. Consol in vivo photosynthesis, PSII activity and ABA content during dehydration

Changes in photosynthetic activity, CO2 assimilation rate, Phi(PSII) by fluorescence and ABA content, were monitored in the grasses Eragrostis curvula cv. Consol and Sporobolus stapfianus Gandoger in response to dehydration. The first being a warm season grass well adapted to drought and the second a desiccation-tolerant or resurrection plant. The trial was performed on intact leaves during a whole plant drying course. After a cycle of dehydration (down to congruent to 5% RWC) and rehydration to full turgor the resurrection plant showed recovery of photosynthetic capability. E. curvula is drought-resistant but not drought-tolerant being not capable of recovering when dried to congruent to 20% RWC. The sensitivity of photosynthesis to the drying treatment was different in E. curvula and S. stapfianus. During drying treatment, up to a leaf water loss of congruent to 40,%, E. curvula photosynthesis seemed to be inhibited by carbon metabolism, because PSII activity was not yet affected. In S. stapfianus at the same point of dehydration photosynthesis still worked though a down-regulation of PSII activity (Fv/Fm) occurred at a higher RWC. Nonphotochemical chlorophyll fluorescence quenching (qN) was analysed. During drying qN increased in both plants, but more in the resurrection plant though its assimilation rate was less affected. The importance of ABA in regulating CO2 assimilation rate is discussed.