Abstract:

In order to explore the effects of different concentration of exogenous GABA on tomato seedlings dry matter accumulation,root development,antioxidant enzyme activities and photosynthetic characteristics under high temperature stress,the tomato variety Fenteli was selected as the test material,and five treatments,including spraying distilled water (CK),1 mmol/L GABA(T1),5 mmol/L GABA(T2),10 mmol/L GABA(T3)and 20 mmol/L GABA (T4),were set up in this study. Spraying once every two days for two consecutive times. After spraying,the seedlings were exposed to high temperature stress at 40 ℃/35 ℃ (day/night),14 h (light)/10 h (dark)with light intensity of 250 μmol/(m²·s)for 7 days. The results showed that compared with CK,spraying GABA with the concentration of 10 mmol/L or less (T1,T2 and T3)significantly promoted the growth of tomato seedlings,and the plant height,stem thickness,aboveground dry weight and seedling index increased by 4.96%—6.92%,7.65%—19.26%,29.41%—52.94%,20.00%—26.67%,respectively. Noteworthy,compared with CK,T2 treatment significantly increased the total root length,total surface area,total volume and tip numbers of root system by 23.04%,13.95%,11.76% and 18.30%,respectively. Moreover,compared with CK,T2 treatment not only increased the leaves activities of SOD,POD and CAT in (increasing by 22.58%,51.73% and 148.80% respectively),but also decreased the relative conductivity and malondialdehyde content (decreasing by 12.84% and 21.89%),and thus significantly increasing the photosynthetic rate,stomatal conductance and transpiration rate of leaves (increasing by 81.38%,36.19% and 41.26% respectively)by ensuring the integrity of the cell membrane structure and function of leaves. However,there were no significance differences for the dry matter accumulation,photosynthetic characteristics and relative conductivity of tomato seedlings under T4 and CK treatments,and even the former inhibited the root development. In a word,our study demonstrated that foliar spraying with an appropriate GABA concentration could alleviate the inhibition of photosynthesis under high temperature stress through protecting the integrity of leaf cell membrane by improving capacity of leaf osmotic adjustment and antioxidant enzyme activities. Additionally,spraying GABA could also improve the heat tolerance of tomato seedlings by promoting dry matter accumulation and root development. The effect of GABA with 5 mmol/L was the best in this study.

Key words: Tomato seedlings, GABA, High temperature stress, Antioxidant enzyme activity, Photosynthetic characteristics