In vitro acclimatization of papaya plantlets to reduced relative humidity and increased irradiance
1991
Dilla, J.A.
Papaya shoot tip cultures were subjected to acclimatization treatments consisting of reduced relative humidity (RH) (approximately 92%), attained through the bottom-cooling method, and/or increased light intensity, using a cool-white flourescent-incandescent lighting combination. An apparent inhibition of stomatal development was observed in treated leaves which had a mean of 50% immature stomates, in contrast to a mean of 92% fully developed stomates in control leaves. Moreover, a significantly improved stomatal physiology, evidenced by narrower stomatal aperture, increased percent closure and lower percent and rate of water loss, was observed in leaves exposed to either reduced RH, increased irradiance or both. In terms of relative water content, leaves exposed to both factors can be considered more acclimatized than the rest of the treatments. Examination of leaf samples under the scanning electron microscope revealed the presence of epicuticular waxes on both leaf surfaces in all treatments. The remarkably large percent water loss and the elevated rate of water loss of control leaves can then be attributed primarily to a high frequency of mature stomates with significantly large aperture and which were incapable of closure. Exposure of plantlets to reduced RH and increased irradiance during their in vitro culture, therefore, delayed stomatal development but conferred improved stomatal response to water stress and, consequently, greater competence for survival under natural environmental conditions.
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