The effect of water stress on the growth rate, water content and proline accumulation in tomato calli and seedlings

This study was conducted on tomato line Apedice and its aw and blsisogenic/near isogenic lines (IL/NILs) to determine the effects of water stress (induced by 10% and 20% PEG-6000) on the growth, water content and proline accumulation at the early seedling growth stage and during callus formation. The experiments in vivo involved monitoring of the water stress on the above mentioned parameters during the stage of "radical protrusion - cotyledon emergence". The results have shown that seedling growth responses (mean number of days to cotyledon emergence and mean length of root and hypocotyl) depend on the genotype and the severity of the stress applied. The data obtained provides evidence that: the seedling stage was a more sensitive indicator of water stress compared with total germination in tomato; root growth is better than hypocotyl growth for evaluating drought tolerance in tomato; and more severe stress treatments get clear information on the effect of genes aw and bls in tomato development under osmotic stress. In the in vitro experiments, callus growth and water content were shown to be negatively related to water stress induced by elevated PEG concentrations, while osmotic adjustment through the accumulation of proline was positively related to the severity of the stress. In this case, anthocyaninless lines showed higher callus growth rates and proline accumulation in comparison with a wild-type line. This study has revealed an enhancing effect of two anthocyaninless mutant genes on tomato growth responses in vivo and in vitro under osmotic stress. The similarity of the data from the experiments both in vivo and in vitro suggested that an alternative screening method involving in vitro culture in a combination with the "proline test" could be a useful and complementary tool for large-scale screening for drought tolerant tomato.