Changes in chlorophyll fluorescence in maize plants with imposed rapid dehydration at different leaf ages

A comparison of the effects of a rapidly imposed water deficit with different leaf ages on chlorophyll a fluorescence and gas exchange was performed in maize (Zea mays L.) plants. The relationships between photosynthesis and leaf relative turgidity (RT) and ion leakage were further investigated. Leaf dehydration substantially decreased net photosynthetic rate (A) and stomatal conductance (G(s)), particularly for older leaves. With dehydration time, F-v /F-m maintained a relatively stable level for youngest leaves but significantly decreased for the older leaves. The electron transport rate (ETR) sharply decreased with intensifying dehydration and remained at lower levels during continuous dehydration. The photochemical quenching of variable chlorophyll fluorescence (q(P)) gradually decreased with dehydration intensity for the older leaves but increased for the youngest leaves, whereas dehydration did not affect the nonphotochemical chlorophyll fluorescence quenching (NPQ) for the youngest leaves but remarkably decreased it for the older leaves. The leaf RT was significantly and positively correlated with its F (v)/F-m, ETR, and q(P), and the leaf ion leakage was significantly and negatively correlated with F-v /F-m and NPQ. Our results suggest that the photosynthetic systems of young and old leaves decline at different rates when exposed to rapid dehydration.