Research progress on the impacts of low light intensity on rice growth and development

Light is an important environmental factor for healthy growth and development of plants. Global warming has increased the occurrence of overcast, rainy and low light intensity. Light stress has been known to adversely affect shade tolerance, healthy growth and development of rice. This paper reviewed research progress on the impact of low light stress on photosynthesis, vegetative growth, yield and quality of rice. Several studied noted that low light stress affected every aspect of vegetative growth (plant height, tiller number, root growth, stoma regulation and chlorophyll development), photosynthesis, dry matter accumulation and partition, and yield and quality of rice. Light not only provided energy for photosynthesis but was also a signal for photomorphogenes. Plant light receptors sensed changes in ambient light signal (including light quantity/fluoresce, quality/wavelength, direction and duration) which correspondingly regulated photomorphogens. Shades induced low light stress in crops. Plant phytochromes detected changes of red/far-red light ratio under shade conditions, leading to a series of changes in morphological traits. These so called shade-avoidance syndrome included accelerated elongation of hypocotyls, internodes and petioles, upward leaf movement (hyponasty), and accelerated flowering and apical dominance. However, shade tolerance lacked classical shade-avoidance syndrome. It also increased specific leaf area, photosystem (PSII︰PSI) ratio, reduced chlorophyll a/b ratio and increased physical defense. There was less research on shade-avoidance syndrome and shade tolerance of rice. The review further discussed how different shade materials affected light quality (wavelength), and how shade-avoidance syndrome was reduced by using rice phytochrome genes and light signal-related transcription factor genes identified in Arabidopsis thaliana. Countermeasures were then suggested to relieve low light stress during rice growth. The problems and prospects of future research in this field were also discussed.