Immature leaves ofWeinmannia racemosaare more heat tolerant than mature leaves based on differences in chlorophyllafluorescence and solute leakage

Abstract

Numerous studies have examined how leaf temperature affects photosynthesis, but few have investigated photosynthetic temperature sensitivity during leaf expansion. Here, we show that immature leaves ( Â18% of final leaf area) of the common New Zealand tree, Weinmannia racemosa L. f. (Cunoniaceae), are less sensitive than mature leaves to rapid increases in leaf temperature (from 25 to 35 8C) as measured by chlorophyll a fluorescence. Relative differences in the tolerance of photosystem II to heat were supported by solute leakage experiments, in which disks from immature leaves incubated at 47 8C lost significantly fewer solutes than did disks from mature leaves. In addition, levels of trienoic (18:3) fatty acids were far lower in immature than in mature leaves (low levels are known to be associated with photosynthetic thermotolerance). The developmental changes in photosynthetic tolerance to heat stress likely correspond to compositional differences of the thylakoid membranes during leaf expansion. This result may be useful in understanding photosynthetic responses to temperature in young leaves which lack functioning stomates, or under extreme conditions when leaf temperatures are high or fluctuate rapidly.

Field‐grown Cotton Exhibits Seasonal Variation in Photosynthetic Heat Tolerance without Exposure to Heat‐stress or Water‐deficit Conditions

“…For example, it has been demonstrated recently that young, not fully expanded, leaves exhibit greater thermal stability than mature leaves on the same plant at certain times during the growing season (Snider et al. , Choinski and Gould , Hall et al. ).…”

“…In contrast with the abundant information on PSII thermal stability, only a limited number of studies have addressed the effect of plant development on heat tolerance under field conditions. For example, it has been demonstrated recently that young, not fully expanded, leaves exhibit greater thermal stability than mature leaves on the same plant at certain times during the growing season (Snider et al 2010b, Choinski and Gould 2010, Hall et al 2014). However, information regarding the impact of plant age on heat tolerance of fully expanded leaves is, to our knowledge, non-existent for field-grown plants.…”