Light is the basic environmental factor of plant growth and development. It is not only the basic energy of photosynthesis, but also an important regulator of plant growth and development. The growth and development of plants are not only restricted by the amount or intensity of light (photon flux density, PFD), but also affected by the light quality, i.e. different wavelengths of light and radiation and their different proportions of composition.
Plants can detect the subtle changes of light quality, light intensity, light duration and direction in the growing environment, and initiate the physiological and morphological changes necessary for survival in this environment. Blue light, red light and far red light play a key role in controlling plant light morphogenesis. Photoreceptors, such as phytochrome (PHY), cryptochrome (cry) and phototropin (phototropin, photo), receive light signals, and initiate changes in plant growth and development through signal transduction.
Red light (R) inhibited internode elongation, promoted lateral branching and tillering, delayed flower differentiation, and increased anthocyanin, chlorophyll and carotenoid. Red light can cause the positive light movement of Arabidopsis root system. Red light plays an active role in plant resistance to biotic and abiotic stresses.
Far red light (FR) can counteract the red light effect in many cases. The low R / FR ratio led to the decrease of photosynthetic capacity. In the growth chamber, the white fluorescent lamp was used as the main light source, and led was used to supplement far red radiation (emission peak 734nm) to reduce the content of anthocyanin, carotenoid and chlorophyll, while the fresh weight, dry weight, stem length, leaf length and leaf width of the plant increased. The growth promoting effect of FR supplementation may be due to the increase of light absorption caused by the increase of leaf area. Arabidopsis plants grown at low R / FR were larger and thicker than those grown at high R / FR, with large biomass and strong cold adaptability. Different proportion of R / FR can also change the salt resistance of plants.
Generally speaking, increasing blue light share in white light can shorten internode, reduce leaf area, reduce relative growth rate and increase n / C ratio.
Blue light is needed for chlorophyll synthesis and chloroplast formation in higher plants, and for the sunny chloroplasts with high chlorophyll a / B ratio and low carotenoid level. Under red light, the photosynthetic rate of P. parachuta cells decreased gradually, and it recovered rapidly after turning to blue light or increasing some blue light under continuous red light. When dark growing tobacco cells were transferred to continuous blue light for three days, the total amount and chlorophyll content of rubulose-1, 5-bisphosphonate carboxylase / oxygenase (Rubisco) increased sharply. In accordance with this, the dry weight of cells in a unit culture medium also increased sharply, while it increased slightly under continuous red light.
The dry weight of tomato seedlings growing under white light (including red, blue and green light) was significantly lower than that under red and blue light. The results of spectral analysis of growth inhibition in tissue culture showed that the most harmful light quality was green light with a peak value of 550nm. The ratio of height, fresh and dry weight of marigold growing under the light without green light
The growth of plants increased by 30% ~ 50%. Full spectrum light complementing green light resulted in plant dwarf and reduced dry and fresh weight. Removing green light can enhance the flowering of marigold, while adding green light can inhibit the flowering of carnation and lettuce.
Yellow light (580 ~ 600nm) inhibited the growth of lettuce. The results showed that only yellow light (580 ~ 600nm) could explain the difference of growth effect between high pressure sodium lamp and metal halide lamp, that is, yellow light inhibited growth. In addition, yellow light (peak at 595nm) inhibited the growth of cucumber more than green light (peak at 520nm).
Some conflicting conclusions about the Yellow / green effect may be due to the different wavelength ranges used in those studies. Moreover, because some researchers classify the light of 500-600nm as green light, there are few literatures about the effect of yellow light (580-600nm) on plant growth and development.