Assessing the drought-resistance adaptive advantage of some anatomical and physiological features in Nicotiana tabacum

Abstract

As part of an extensive research programme that attempts to explain and quantify the known difference in drought tolerance of four Nicotiana tabacum L. cultivars, some aspects that may contribute towards the avoidance and tolerance of drought stress were investigated to evaluate overall resistance. The results presented emphasize the adaptive significance of effective leaf movements in determining drought tolerance, by reducing or preventing damage to the photosynthetic system caused by photoinhibition and direct heat damage. Leaf movement seemed to be achieved with greater efficiency by the drought-tolerant cultivars GS46 and Elsoma. Drought stress specifically influenced the carotenoid composition. A strong quantitative correlation existed between the formation of zeaxanthin in the xanthophyll cycle and the type of fluorescence quenching, which is indicative of nonradiative energy dissipation. The latter occurred to a lesser extent in the drought-tolerant cultivars GS46 and Elsoma. This phenomenon also indicated that the rate constant for nonradiative energy dissipation in tobacco remains relatively small in relation to the rate constant for fluorescence during drought stress. Furthermore, irrespective of their drought tolerance, it would seem that tobacco plants have a capability towards starch overproduction, though this was less pronounced in the drought-sensitive cultivars TL33 and CDL28. Owing to anatomical differences, resistance to water flow varied between the respective cultivars, as did the percentage intercellular spaces, both of which correlated positively with the slower decrease in water use efficiency and faster recovery upon rehydration of the drought-tolerant cultivars. Key words: carotenoid composition, chlorophyll a fluorescence, Nicotiana tabacum L., mesophyll surface area, leaf movements.