Effect of light on growth and chlorophyll development in kiwifruit ex vitro and in vitro

• •kiwifruit cultivars have great flexibility and high capacity for acclimation to high-light environments. • •kiwifruit is sensitive to light quality; blue light promotes the accumulation of chlorophyll, carbon and carbon/nitrogen ratio, as well as the numbers of guard cell plastids, while red light stimulates the growth and development of kiwifruit and improve the starch and sugar contents of leaves. • •The optimal blue light / red light ratio is deemed to be species-specific in kiwifruit. Light is one of the most important environmental factors that strongly mediates plant physiological and morphological development. Few studies have investigated the effect of light on perennial fruit crops, which have long generation times and are large in size, that complicates the evaluation of plant responses to light in controlled environments. This study assessed the impact of light intensity on chlorophyll (Chl) variation in 41 kiwifruit cultivars during the growing season, and examined the physiological, morphological and gene expression changes of kiwifruit plantlets in vitro under different light qualities treatments, such as white light, red light (RL), blue light (BL) and a mixture of RL and BL with different ratios. The Chl content in 24.4% of kiwifruit varieties increased continuously with increasing sunlight intensity from April to August; but 34.15% of varieties remained unchanged and 41.5% of varieties decreased in July and August when kiwifruit plants were exposed to maximum solar radiation density and duration. The controlling experiment of light qualities showed that blue light was effective for the induction and accumulation of kiwifruit Chl contents and carbon nitrogen ratio (C/N ratio), as well as the numbers of guard cell plastids, whereas red light induced plant vegetative growth and increased starch and sucrose content in leaves. Furthermore, blue light induced higher expression of key genes for Chl biosynthesis than red light. These results indicate that kiwifruit plants exhibit strong morphological plasticity induced by light, and the development of kiwifruit can be induced by culturing the plants in vitro under a combination of BL and RL.