Growth and Physiology Of The 7B-1 Tomato Mutant Under Water Deficit

Drought causes large declines in crop yields, thus plaguing farmers and threatening food security. Plant physiologists have attempted to produce drought-tolerant crops through an understanding of the plant hormone abscisic acid (ABA). The 7B-1 ABA overproducing tomato mutant was proposed to be drought-tolerant in experimental treatments on seedlings. Our study focused on drought tolerance in the more agronomically important vegetative and pre-flowering stages of the plant. We tested the following hypotheses: 7B-1 would withstand the effects of drought on retarding plant growth, 7B-1 would show osmotic adjustment, and maintenance of water potential and turgor. In addition, we aimed to understand the physiological implications of a high endogenous level of ABA by measuring biomass, growth rate, and transpiration. Our findings show the growth of stems and leaves in 7B-1 is more inhibited than WT when water is limiting (p<0.01, respectively). 7B-1 and WT show similar osmotic adjustment values (p>0.05), but 7B-1 cannot maintain adequate turgor when compared to the WT (p<0.05) due to its lower leaf water potential (p<0.05). Thus, we concluded 7B-1 is unable to tolerate a gradual decline in water availability. However, the mutant exhibited a greater shoot growth rate and biomass than WT when well-watered (p<0.01, respectively), which can be explained by the mutant’s larger epidermal cell size (p<0.05). Interestingly, 7B-1’s significantly lower transpiration rate (p<0.05) does not restrain its biomass accumulation. This research reveals a higher endogenous level of ABA does not automatically confer drought tolerance.