The Growth, Leaf Antioxidant Enzymes and Amino Acid Content of Tomato as Affected by Grafting on Wild Tomato Rootstocks 1 (S. Pimpinellifolium and S. Habrochaites) Under Salt Stress

Abstract

Salinity in soil or water is a serious threat to plant growth, which reduces yields and threatens food security. It is possible to reduce the negative effects of salinity on tomato scions through grafting. To evaluate the effects of salt stress on graft combinations in hydroponic conditions, SP3, SP4, SP5 (S. pimpinellifolium), SH1, SH3, SH5 (S. habrochaites) and two hybrids L × SP5 (S. lycopersicum L. × S. pimpinellifolium) and L × SH3 (S. lycopersicum L. × S. habrochaites) were used as rootstock and two varieties Galaxy and H2274 (S. lycopersicum L.) were used as scion. Plants were evaluated in terms of biomass parameters and antioxidant enzyme activities and amino acid contents in leaf tissues under control and salt stress conditions. Salt stress decreased the fresh weight of shoots and roots by 68.71 and 23.59, respectively, and increased H2O2 content (93.90 %) and MDA content (63.71 %). In addition, salt stress in leaf tissues POD (204.49 %), CAT (83.87 %), SOD (204.49 %), GR (88.23 %), GST (100.16 %), G6PD (32.85 %), 6GPD (46.19 %), APX (157.29 %) caused an increase in enzymes and total amino acid content (160.57 %). In salt stress conditions, SH5/Galaxy and L × SP5/Galaxy are the graft combinations with the highest fresh shoot and root weight, leaf number and root volume. These graft combinations contain the most isoleucine, proline lysine, alanine arginine, sucrosine leucine, methionine, hydroxyproline glutamate, glutamine and histidine amino acids in leaf tissues and have the lowest MDA content. Ungrafted H2274 and Galaxy plants have the highest MDA and content under salt stress conditions, these ungrafted plants have the least other amino acids and enzymes other than theonine amino acid in their leaf tissues. Furthermore, ungrafted plants under saline conditions had the lowest shoot and root fresh weight, leaf number and root volume. MDA content correlated negatively with shoot and root fresh weight, leaf number and root volume. H2O2 correlated positively with CAT, SOD, GST and peroxidase enzymes and negatively with APX, GR and G6PD enzymes. It seems that the antioxidant enzyme activity and amino acid content in leaf tissues influence salinity response and the appropriate rootstock/scion combination could be a viable method for tomato cultivation in saline conditions.