Physiological Adaptive Strategies of Oil Seed Crop Ricinus communis Early Seedlings (Cotyledon vs. True Leaf) Under Salt and Alkali Stresses: From the Growth, Photosynthesis and Chlorophyll Fluorescence.

Yingnan Wang,Xiufeng Yan,Zhiqiang Zhou,Jixiang Lin,Xiaoyuan Peng,Weiguang Jie,Xiaoyu Hua

doi:10.3389/fpls.2018.01939

Abstract

Ricinus communis is an important energy crop and is considered as one of the most potential plants for salt-alkali soil improvement in Northeast China. Early seedling stage (such as the cotyledon expansion stage) is always a vulnerable stage but plays a vital role in plant establishment, especially under stress conditions. However, little information exists concerning the function of cotyledon and the relationship between cotyledon and true leaf in the adaptation to salt stress and alkali stress of this species. Here, Ricinus communis seedlings were treated with varying (40, 80 and 120 mM) salinity (NaCl) and alkalinity (NaHCO3), growth, photosynthesis, and chlorophyll fluorescence of cotyledons and true leaves were measured. The results showed that the biomass, photosynthetic parameters, and the qp value of both cotyledons and true leaves decreased with increasing salt-alkali stress, and the decrease in biomass, gs and Tr, of true leaves were much greater than that of cotyledons. Salt-alkali stress only reduced photosynthetic pigments and ΦPSII in cotyledons, but did not affect those in true leaves. Additionally, the Fv/Fm and NPQ between cotyledons and true leaves showed different trends in salinity and alkalinity. The results suggested that alkali stress could cause much more damage to the castor bean seedlings, and different physiological responses and adaptive strategies are found in cotyledons and true leaves under salt-alkali stress. This study will help us develop a better understanding of the adaptation mechanisms of cotyledon and true leaf during early seedling stage of castor bean plant, and also provide new insights into the function of cotyledon in Ricinus communis under salt-alkali stress conditions.

Highlights

Soil salinization and alkalization have been considered as major environmental threats to the agricultural system
We evaluated the effects of salt-alkali stress on the early seedlings of castor bean (Ricinus communis) from the perspective of seedling growth, photosynthesis and chlorophyll fluorescence
Three-way ANOVA results showed that the fresh weight (FW), dry weights (DW), and Water content (WC) of castor bean seedlings were affected by plant tissue, salinity concentration, and stress type, but were not affected by interactions of the three factors (Table 1)

Summary

Introduction

Soil salinization and alkalization have been considered as major environmental threats to the agricultural system. They inhibit crop growth, and cause land degradation (Lin et al, 2014; Guo et al, 2015). Alkali stress has the impacts of a high pH level in addition to the same stress features as salt stress, which can inhibit nutrient absorption and result in ionic imbalance in plant cells (Wang H. et al, 2011). To the best of our knowledge, the majority of reports in this field only emphasized the physiological effects of salt stress, with little attention to the alkali stress

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