Photomorphogenesis And Physiology Of Tomato Seedlings In Response To UVA Radiation

Plant growth need light not only for photosynthesis but also sense various light signals by photoreceptors for photomorphogenesis.UVA(315-400 nm)is the main component of solar UV radiation reaching the Earth‘s surface(95%).UVA shares same photoreceptors with blue light(400-500 nm),while its function in plant physiology is largely unknown.With the technology bottleneck of UV LEDs,it‘s difficult to obtain suitable UVA lights for research,previously.Fortunately,UVA LED light products have been gradually market-oriented in recent years,which provides different spectrum wavelength UVA lights guarantee for further study.It is a right time to carry out a systematic study to explore the effects of UVA radiation on plant photomorphogenesis,secondary metabolism,photosynthesis,and other growth processes.Meanwhile,clarifying the function of UVA can also provide a theoretical basis for developing new LEDs for indoor plant production.In this study,we compared the effects of UVA and blue light under the background of pure red light on the various response of tomato seedlings.Here are the main contents of this study:1.Tomato seedlings were grown in a climate room under the light intensity of 200?mol m^-2 s^-1with five light treatments were set:the combinations of UVA and blue light with peak wavelengths of 370/385/400/450 nm with red light(UVA/blue:red=1:9),with the pure red light treatment as control.Compared with pure red light,UVA of different wavelength and blue light increased the shoot weight accumulation and promoted the increase of leaf thickness and chlorophyll content.However,the morphogenesis induced by UVA was different from that of blue light.UVA increased leaf area,but the inhibition effect on stem elongation was weaker than that of blue light.Under pure red light background,blue and UVA of different wavelengths promoted total phenolic and flavonoids accumulation beside 370 nm UVA?2.Tomato seedlings were grown in a climate room under the light intensity of 250?mol m^-2 s^-1with four light treatments were set:the combined treatment of low(UVA:red=1:15)and high dose(UVA:red=1:7)with wave peak of 370nm and red light(UVA:red=1:7),the combined treatment of blue with red light(blue:red=1:7),with the pure red light treatment as control.Different doses of R+UVA treatments promoted the petiole up-warping and leaf flattening and improved the light interception of tomato plants.The morphology response might be related to IAA and brassinolide signals.In addition,the function of UVA in maintaining the photosynthetic capacity of leaves was similar to that of blue light.3.Tomato seedlings were grown in a climate room under the light intensity of 200?mol m^-2 s^-1with five light treatments were set:the combined treatment of different wavelength UVA and blue light with wave peak of 370/400/450 nm with red light(UVA/blue:red=1:9),the combined treatment of 200?mol m^-2 s^-1red light plus 1?mol m^-2 s^-1blue light as the low blue light treatment,with the pure red light treatment as control.Compared with pure red light,the promoting effect of 370nm UVA on leaf flattening process was greater than that of 400 nm UVA.Low blue light treatment induced similar morphological changes on leaf expansion to that of normal blue light,but still weaker than that of UVA treatment.These results indicated that the morphological changes caused by UVA signal was not be attributed to a?low blue light?signal.Both UVA and blue light induced morphological changes of leaves depending on auxin transportation.4.Tomato seedlings adapted to pure red light for 5 days and then were transferred to the combined treatment of different wavelength UVA and blue light with wave peak of 370/450 nm with red light(UVA or blue:red=1:9),with the pure red light treatment as control.Leaf flatting process was greater promoted by UVA light than that of blue in 48 hours after the transferring.The transcriptome analysis showed that UVA and blue light had different effects on gene expression patterns under pure red-light background.Compared with blue light signal,UVA signal promoted the expressions of auxin response family of SAURs and IAA,and showed no repress on gibberellin signaling,which resulted the promotion of the expression of gene coding cell wall biogenesis and expansion.The results indicated that UVA could promote tomato seedling growth,and replace blue light signal to promote plant photosynthesis and secondary metabolism.Differing from that of blue light,UVA light promoted the petiole upwarping and leaf flattening and resulted in the improving light interception of tomato plants,which depending on auxin transportation and signals.Our result suggests that UVA cannot be unequivocally considered as an abiotic stress factor,and may provide the basis for future recipes for growing plants with artificial light.