The growth of crop roots is affected by the light
Light has always been an important factor affecting the development of crops. So does light affect the production of crop roots? In order to conduct in-depth studies on light-crop roots, to further understand the intrinsic connections between crops and roots, and to reveal the physiological significance of light during the entire growth and development of crops, the authors reviewed the literature on the effects of light on crop roots in order to The research and guidance of high-yield, high-quality cultivation of crops.
1 Effect of illumination on crop roots
People used different light levels early to test the different responses of crop roots to light. According to reports, light affects the growth and development of radish (Raphanussativus L), pea (Pisumsativum L), cucumber (Cucumissativus L) and other crops in vitro roots. After dark pretreatment of young stems of Vicia faba L, stem adventitious root ratio was nearly 4 times higher than light pretreatment, and dark pretreated adventitious roots had an intragenous origin. The root biomass (dry weight) of the seedlings of Gordonia szechwanensis Chang and the biomass of the coarse root, middle root, and fine root were decreased with increasing shading intensity. The rooting ability of rice (Oryza sativa L) seedlings was stronger under strong light and weaker under weak light; root growth was larger under strong light and smaller under weak light. Zea mays L seedlings have high photosynthetic rate, respiration rate, and material production ability under high light conditions. The dry matter distributed to the roots in the shoots also increased significantly, showing the dry root weight, total root volume, and total root mass per plant. Long and other forms, quantitative indicators have increased significantly, the root to shoot ratio of plants increased. In order to maximize the overall light effect of crops, people have paid more attention to the effects of low temperature and low light in recent years. Relevant studies have pointed out that the effects of low temperature and low light on plant shoots and roots are different, which results in a decrease in dry weight of tomato (Ly-copersiconesculentum Mill) shoots, but does not reduce root dry weight.
While studying the effects of light on crop root morphology and quantitative traits, more physiological and biochemical studies have emerged. Studies have shown that light can promote the exchange of crop shoots and roots. In herbaceous plants, light can be modulated by the phytochrome (Phy) through the internal light environment and propagated from the aerial parts to the root system and regulate its growth and development. Nitrate reductase (NR) is a light-induced enzyme, and light irradiation promotes the synthesis of NR. The NR activity in the roots of four-week-old wheat (Triticumaestivum L) seedlings grown under different light irradiances increased with the increase of light intensity, and there was a positive correlation between illuminance and NR activity. The effects of different low temperature and low light treatments on the root activity of plants were not consistent. It has been reported that low light treatment does not affect tomato root activity. The reason may be related to the strong resistance of tomato roots to stress.
However, other relevant experiments showed that when the root vigor of tomato control plants remained relatively stable, low temperature and weak light treatment resulted in a rapid decline in root vigor; in the process of root vigor recovery, it was more likely to recover to its original level when the temperature was higher. The time required is also shorter; at the same time, low-temperature and low-light treatment also enhances the activities of superoxide dismutase (SOD) and peroxidase (POD) in tomato roots, and rapidly reduces the activity of catalase (CAT) in roots. Strong light can increase the absorption rate of NH4+ or NO3- in rice seedlings and wheat roots. Rice seedlings cultivated under strong light have high protein nitrogen content in their roots, low protein nitrogen content, high total nitrogen content, and high protein nitrogen/total nitrogen ratio. It can be seen that strong light can increase the synthesis of nitrogen compounds in rice seedlings and promote the accumulation of proteins in roots. Under different illumination conditions, the expression of GS isozyme glutathione synthetase (GS) in rice roots was not affected.
2 Effect of illumination time on crop roots
Sufficient light contributes to photosynthesis, which makes it possible to transfer more of the photosynthate produced in the above ground to the root system, thus laying the foundation for the development of a robust root system. Reports have shown that prolonging the photoperiod (increasing the amount of light) is beneficial to the rooting of Capsicunannuum L; and OpuntiadilleniiHaw (OpuntiadilleniiHaw) under the condition of insufficient illumination (less light), the rooting time is prolonged, the growth and development are slow, and the aboveground part is also easy. deformity. When spring wheat and spring barley (Hordeum vulgare L) are used for light treatment, the length of the roots of plants without shading (large amount of light) is short, and the length of the roots of shading (less light) is long. However, other studies have shown that the growth of rice seedling roots is promoted by the decrease in the amount of light. Under different shading conditions, the activity of succinate dehydrogenase (SDH) in ginger (Zingiberofficinale Rosc) roots increased with increasing degree of shading, and this contributed to the increase of root vigor. Another study pointed out that when using LED light-emitting diodes as a light source material to illuminate the crop roots, the root/shoot ratio of the plant can be observed to increase, and the dry matter weight of the aerial parts increases.
3 Influence of light quality on crop roots
With the gradual deepening of the understanding of the entire light, people have carried out research on the impact of different light quality on crop roots. Although not directly exposed to light, the root system responds differently to different light qualities. For example, the rice seedlings cultivated under the blue light irradiation have more hair roots than the rice seedlings cultivated under the red light or the white light irradiation, and the roots are thick and the root biomass is large. OHNO et al. further observed that white light inhibited the elongation of rice root cells, while blue light promoted cell elongation. For another example, compared with control white light, red light and red-blue light can significantly promote the growth and development of roots of Cucumismelo L, with high root induction rate and strong growth potential. Especially under red light conditions, the rooting rate is as high as 100%. For example, different light qualities have different effects on the root growth of Eucommia ulmoides Oliv, which is mainly manifested in the strength of red light, followed by Huang Guang, Green light. Under the same kind of light color film, the average number of root buds is very close regardless of whether the average spectral transmittance is large or small, except for the blue film, the total length of each bud also shows the same change rule. This reflects that the root sprouting ability of the root is mainly controlled by light quality. In the experiment of oats (Avenasativa L), the plants irradiated with blue light and violet light were shorter, but their root systems were more developed than the control group. The number of hair roots was 1114% and 1171% of the control group, respectively. The inhibition was the strongest, followed by red light and white light; different light qualities all promoted the synthesis of anthocyanins (ACN) in isolated roots, of which white light had the most obvious effect, followed by blue light and red light. However, in the culture of cucumber roots in vitro, photoinhibition of root growth, of which the inhibition of white light is the strongest, followed by blue and red light.
Under different light quality conditions, the dehydrogenase activity (DHA) in roots of spring wheat during tillering was significantly different. The average blue light treatment was 1205% higher than that of the white light control, and the purple, blue and red light treatments were increased by 1369% and 597% respectively. In the experiment, similar results were also obtained. Under strong light or blue light irradiation conditions, the oxidative power of A-naphthylamine in roots of rice seedlings or CAT activity in roots was higher than that in low light or under red or white light conditions. seedling. In addition, blue light also increased the absorption rate of NH4+ or NO3- in the roots of rice seedlings and wheat seedlings, and increased the protein nitrogen content accumulated in roots. Thus, blue light promotes the synthesis of nitrogen compounds in rice seedlings and the accumulation of proteins in roots. In addition, the synthesis of chlorophyll is affected when wheat roots are irradiated with red light (300-500 Lmol#m-2#s-1) for a long time.
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