S-adenosylmethionine Decarboxylase Gene Functions In Ca²⁺-dependent Response Of Peanut To Salt Stress

Peanut (Arachis hypogaea), a kind of calcium-needed plant, is one of the important oil crops in China, which has a very high nutritional value and economic value. Arable area is shrinking with the water crisis all around the world and overly high soil salinity. It is necessary to open up new planting area, such as saline soil, for peanut without competitions between grain and peanut production. But salt stress and exchangeable calcium deficiency in saline soil have become important factors influencing the peanut growth and leading to the loss of peanut production. It is required to explore peanut salt-tolerant molecular mechanism and improving peanut salt resistance, in order to solve land conflicts between the peanut with grains, and increase the development and utilization of saline land. Our experiments studied the effects of calcium on salt stress to peanuts and the effects of SAMDC, a key enzyme of polyamine synthesis way in the peanut on salt stress. We transferred peanut SAMDC gene into tobacco using genetic engineering and studied the salt resistance of transgenic tobacco.Huayu 22, one of the peanut cultivar, were cultured with Hogland solution with 0 mmol·L-1 Ca2+ (CK) and 6 mmol·L-1 Ca2+ (6CA), respectively, combined with CPZ, a CaM antagonist, EGTA, a calcium ion chelating agent, and LaCl3, a calcium ion channel inhibitor, which studied the influence of the calcium on peanut seedling to.salt stress. The results showed that the presence of calcium ions can improve antioxidant enzyme activity of peanut systems, improve resistance to oxidative stress, and increase osmotic adjustment ability to enhance resistance of peanut seedling to salt stress.Salt stress induced the expression of AhSAMDC, and the expression of AhSAMDC in 6CA is more than that in CK. AhSAMDC expression is suppressed after 6CA was processed with calcium related inhibitors. Furthermore,6CA has high levels of Spd and Spm concentrations than CK under salt stress. So we suggest Ca2+is likely to be involved in the AhSAMDC transcription process.Methylglyoxal-bis guanylhydrazone (MGBG) is a SAMDC enzyme activity inhibitor. Applying MGBG resulted in the block of polyamine synthesis way.6CA foliar-sprayed with lmM MGBG showed high level leaf relative conductivity and MDA content compared to 6CA foliar-sprayed with water under salt stress. Exogenous polyamines can improve the salt resistance of peanut seedlings to a certain extent. These results suggest that polyamine synthesis can improve the salt resistance of peanuts.AhSAMDC can improve seed germination of transgenic tobacco under salt stress, and promote the growth of transgenic tobacco root under salt stress. Compared with the wild type, AhSAMDC transgenic seedlings have higher antioxidant enzyme activities and osmotic adjustment ability, lighter membrane damage under salt stress, indicating AhSAMDC can improve the salt tolerance of tobacco. Calcium-related inhibitors increased cell membrane damage of tobacco leaves, while AhSAMDC can ease membrane damage, indicating that synthesis of polyamines may direct response to salt stress, and Ca2+ may regulate polyamine biosynthesis by regulating the expression of SAMDC to improve polyamine content so that plant salt resistance is enhanced.