Abstract
The possible causal relationship between the percentage intercellular spaces in the leaf palisade parenchyma and water use efficiency (WUE) was investigated in related Nicotiana tabacum L. genotypes grown under controlled environmental conditions. Experimental observations included the initial quantification of the percentage intercellular spaces, and the measurement of gas exchange by infra-red gas analysis prior to, during, and after recovery from drought stress. Statistically significant differences in the percentage intercellular spaces per surface area existed between the respective genotypes. The percentage intercellular spaces correlated positively with the pre-stress photosynthetic and transpiration rates, as well as with the WUE of drought-stressed plants, but negatively with the WUE of recovered plants and the rate of stomatal conductance during and after drought stress. It is concluded that in air-cured tobacco, high pre-stress photosynthetic rates are accompanied by high transpiration rates in genotypes with a high percentage of intercellular spaces. This discourages use of the former in drought tolerance selection programmes, as used in the past, while selection on the basis of a smaller percentage intercellular spaces would seem to be a more valid screening parameter. This contention is supported by data which indicate that the genotypes with a high percentage intercellular spaces maintain a higher degree of WUE when drought-stressed by sharply decreasing their stomatal conductance, but, contrary to the genotypes with a lower percentage intercellular spaces, they are unable to reachieve or exceed their pre-stress WUE when rewatered.
Published Version
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