Effects of Salt and Water Stresses on Osmotic Adjustment and Osmotica Accumulation in Aloe vera Seedlings

Aloe seedlings were treated with different concentrations of NaCl and iso-osmotic PEG6000 solutions for 10 d, and relative growth rate, leaf thickness, content of main organic solutes, inorganic ions and osmoregulation ability of leaves were determined. The results showed that exposure to - 0.44,- 0.88 MPa NaCl and PEG lowered the relative growth rate(Fig.1A) of aloe leaves and made their thickness smaller (Fig.1B). The growth of seedlings and water content in leaves (Fig.2A) under salt stress were decreased more than that under iso-osmotic water stress. The osmoregulation of aloe seedlings increased with the extent of lowering of osmotic potential of treatment solution and was stronger under -0.88 MPa PEG treatment than under NaCl treatment with the same osmotic potential(Fig.2B). The main osmoregulatory substances of aloe seedlings were soluble sugars,organic acids,K +,Ca 2+ ,and Cl -(Fig.3A). Organic solute contents of -0.88 MPa PEG-treated seedling leaves were dramatically more than that of -0.88 MPa NaCl-treated ones (Fig.3B). Strong osmotic adjustment ability of aloe under PEG stress was mainly caused by accumulation of organic solutes.