Effect of light quality on the growth of in vitro seedling of ‘Qiuhongbao’ grape

Abstract:【Objective】Light is one of the environmental factors affecting tissue culture for propagation. Light quality plays an important role in the growth, physiology and metabolite accumulation in in vitroseedlings. LED polychromatic light can promote the proliferation of in vitro seedlings. At present, the research of light quality on grape growth focuses mostly on vines grown in greenhouse, but there is lit- tle research on its application in tissue culture. Therefore, this study explored the effect of light quality on the growth and physiological characteristics of‘Qiuhongbao’grape seedlings grown in vitro.【Methods】Seven different light quality treatments were set up in this experiment. They were white light (W), red light (R), blue light (B), and combinations of red, blue or white light with different ratios (R∶B=3∶1, R∶B=4∶1, R∶B=5∶1, and R∶B∶W=3∶1∶1). The young stems of‘Qiuhongbao’grape were collected from the Horticultural Station of Shanxi Agricultural University. Healthy young stem segments of‘Qi- uhongbao’were collected in the morning before dew dried. They were washed with water for 2 h to re- move dust, cut it into 5 cm stem segments as explant, and surface disinfected in an ultra clean work- bench. The specific disinfection method was 75% alcohol immersion for 30 s, washing with sterile wa-ter for 2-3 times, 0.1% mercuric chloride immersion, and washing with sterile water for 5 times. The sterilized stem segments were cut into 2 cm single bud stem segments with both ends removed, and in- oculated on MS+0.2 mg·L-1 IBA+1.0 mg·L-1 6-BA+0.2 mg·L-1 NAA+30.0 g·L-1 sucrose + 7.0 g·L-1agar (pH 5.8-6.0). The culture environment temperature was (25±1) °C, and the photoperiod was 16/8 h (light/dark). 10 days after inoculation, the survival rate, pollution rate and browning rate under different treatments were recorded. In each treatment, 10 plantlets were randomly selected to measure seedling water content and their morphological indexes including plant height, stem diameter, leaf number, leaf length, leaf width, root number, maximum root length and internode length. Then the chlorophyll con- tent (ethanol extraction method), soluble sugar content (anthrone method), soluble protein content (Coo- massie brilliant blue method), malondialdehyde (MDA) content (thiobarbituric acid method), and activi- ties of POD (guaiacol method), SOD (NBT photoreduction method) and CAT (H2O2 method) were mea- sured.【Results】The survival rate in R∶B=5∶1 and W treatments was the highest and significantly high- er than the other light treatments, while the pollution rate and browning rate were significantly lower than the other treatments. The plant height in R and W was significantly higher than that in the other treatments. Among different red and blue light ratios, seedling height showed a gradual upward trend with the increase in the proportion of red light. Under the treatment of R∶B=5∶1, the length and width of leaves were the largest. The number of roots and maximum root length of plants under B treatment was the highest, which indicated that single blue light had a strong influence on the rooting of in vitroseedlings of‘Qiuhongbao’. The plant height, internode length, leaf number, leaf length, leaf width, root number and maximum root length were lowest under R∶B=4∶1. There was no significant difference in water content among treatments. Total chlorophyll, chlorophyll a, chlorophyll b and carotenoid contents were the highest in B treatment and significantly higher than in the other treatments. The total chloro- phyll content of leaves under R∶B=5∶1 was significantly higher than that in the other treatments except for B. SOD activity in the leaves was the highest in the treatment of R∶B=4∶1 (100.89 U · g-1 · min-1) and significantly higher than the other treatments, and the second highest was found in the treatment of R∶B=5∶1. The POD activity of leaves was the highest (185.57 U · g-1 · min-1) under R∶B=5∶1, but not signif- icantly different from that under B treatment. The highest CAT activity was 96.27 U · g- 1 · min- 1, which was significantly higher than the other treatments. MDA content of the leaves under R∶B=3∶1 treat- ment was the largest (54.27 U·g-1), and it showed a significant decreasing trend with the increase in red light proportion. The physiological and biochemical data were standardized and analyzed by grey corre- lation, the order of suitability of light treatments for the growth of in vitro‘Qiuhongbao’plantlet was R∶B=5∶1>B>W>R>R∶B∶W=3∶1∶1>R∶B=4∶1>R∶B=3∶1.【Conclusion】R∶B=5∶1 can be used as the optimal light quality ratio to promote the growth of in vitro cultured seedling of‘Qiuhongbao’grape. Total chlorophyll content, maximum root length, plant height, leaf length, and SOD activity are the main indexes that are closely correlated with the growth of the in vitro seedlings of‘Qiuhongbao’under different light quality.