Influences of Soda Soil on the Ultrastructure and Storage Inclusions of Chloroplasts of &amp;lt;i&amp;gt;Syringa oblata&amp;lt;/i&amp;gt; Lindl.

Ziguo Zhao,Fengjuan Zhao

doi:10.4236/nr.2019.109022

Abstract

With a high pH value, soda soil restricts the growth of plants. It had previously been assumed that the inhibition of plant growth by neutral salt stress was partly due to the changes of the ultrastructure and storage inclusions of chloroplasts. The aim of this paper is to investigate the effects of alkali-salt mixed stress of soda soil on chloroplasts of higher plant Syringa oblata Lindl. Testing S. oblata plants had grown for more than five years in soda soil, and transmission electron microscope was used for determining the ultrastructure and storage inclusions of chloroplasts. The results showed that some chloroplasts were destroyed, the normal chloroplasts became smaller, and the envelopes of the functional chloroplasts were slightly expanded generally in soda-stressed plants. The most noteworthy fact was that much more starchgrains accumulated in the chloroplasts of S. oblata growing in soda soil than in neutral soil. The total contents of plastoglobules in chloroplasts did not change considerably, and plastoglobules with different electron densities appeared in chloroplasts in the plants growing in soda soil. We presume that the reduction of the volume and number of functional chloroplasts and the occupation of carbon resources by starch grains accumulated in chloroplasts were the possible reasons for the inhibition of S. oblata growth by soda soil. The accumulation of starch grains was one of the adaptive traits of S. oblata, which promoted the survival of plants in soda soil for that the starch grains could serve as a steady source of soluble sugars, which were known as protectors of plant cells under stressed conditions. Soda soil did not significantly change the total content of plastoglobules in chloroplasts, but changed their compositions.

Highlights

Soil salinization is a severe environmental problem
It had previously been assumed that the inhibition of plant growth by neutral salt stress was partly due to the changes of the ultrastructure and storage inclusions of chloroplasts
The focus of the present study on chloroplasts of S. oblata was determined by two considerations: 1) though with a relatively low growth rate compared with S. oblata growing in neutral soil, S. oblata could grow well in soda soil on the trial base, and 2) as the primary site of photosynthesis, chloroplasts play an important role in plant growth

Summary

Introduction

Soil salinization is a severe environmental problem. According to the data from the United Nations Environment Program, approximately 20% of total agricultural land in the world is salt-stressed [1] [2]. To exploit saline soil and protect the environment, it is a feasible way to grow salt tolerant plants in salt stressed regions [9] [10]. In order to study the adaptability of woody plants to soda soil and the influences of the environmental stress on the growth of plants, and to screen plant varieties adapt to growing in soda soil, we founded a trial base on soda soil in the suburb of Baicheng in the west of Songnen Plain in 2016, and planted dozens of species of salt tolerant woody plants, including Syringa oblata. The focus of the present study on chloroplasts of S. oblata was determined by two considerations: 1) though with a relatively low growth rate compared with S. oblata growing in neutral soil, S. oblata could grow well in soda soil on the trial base, and 2) as the primary site of photosynthesis, chloroplasts play an important role in plant growth. Soil samples were taken from the habitats of testing and control plants, and the pH and electric conductivity of the soil solutions were determined

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