Effects Of Red And Blue Light On Potato-seed Weight And Its Physiological Mechanism In Plant Factories

Potato(Solanum tuberosum L.)ranks the fourth in food crop production.The production of virus-free pre-elite potato-seeds(potato-seeds)is one of the main links to expand potato production.Due to natural climate restrictions,soil-borne diseases and severe continuous cropping obstacles,breeding bases to support potato seed production are limited.With the development of plant factories,crops can grow according to artificial environment control systems and ideal cultivation managements.Plant factories will be a new direction for the production of potato-seeds.Artificial light systems are essential in plant factories.It has a primary role to study the physiological mechanisms of red and blue light about potato growth and potato-seed yield,which can provide the important theoretical basis of artifical light systems to product potato-seeds in plant factories.This research mainly focused on the regulation of potato leaf growth,the metabolism of photosynthethates,the biomass accumulation of potato-seeds,and the distribution of photosynthethates.The purpose is to clarify the regulation mechanisms of the red and blue light on the field formation of potato-seeds,thus providing theoretical basis,technical support and reference for plant factories to produce potato-seeds.In this study,Solanum tuberosum L.cv.Favorita was selected for the experiments.The virus-free potato plantlets were transplanted in plant factories.Plants were under red and/or blue light during 90 days.The whole spectra treatme1ts were under 300 μmol m-2s-1 with a 11/13-h(light/dark)photoperiod.The main results were shown as follows:1.To clarify the physiological mechanism of red and blue light regulating biomass accumulation process in potato-seedsPotato seedlings under W(White light)and RB(50%Red+50%Blue light)showed active metabolism of sucrose and starch and increased shoot growth at 20 d,thus forming potato-seeds ealier than those under R and B treatments.The photosynthesis efficiency,ΦPSII and ETR of leaves under B were significantly higher than those under R at 30 d.The leaves under B upregulated the expression of the potato sucrose transporter 1 encoding gene(StSUT1)and the tuberization signal(StSP6A)at 40 d,promoting the outward transportation of sucrose from leaves and the expression of tuberization signals.The potato-seeds under B increased starch synthesis by upregulating the expression of the sucrose synthase encoding gene(SuSy4)and adenosine diphosphate glucose pyrophosphorylase encoding gene(APL2).The plants under B showed high biomass accumulation during 40-60 d.This resulted in no significant difference in potato-seed yield per plant between B and RB treatments,which was significantly higher than that under W.The potato-seed growth cycle under RB was shorter than that under B,thus taking advantage of potato-seed production in plant factories.Meanwhile,BW treatments(blue light,200 μmo1 m-2 s-1;white light,100 μmol m-2 s-1)also showed that potato-seeds accelerated biomass accumulation.Potato leaves under R promoted excessive accumulation of starch and inhibited leaves from transporting carbohydrates outward.The feedback inhibited photosynthesis and carbohydrate metabolism.With the potato-seed bulking,the excessive accumulation of starch in leaves took advantage of supporting the demand of potato-seed development.At 60 d,leaves under R significantly increased the expression of StSUT1 to promote the outward transportation of photosynthates;and downregulated the expression of APL2 to reduce the excessive accumulation of starch.At the late stage of plant growth(60-90 d),the leaf dry weight under R increased by 21.27%,and the leaf area decreased the least(33.07%)among all treatments.Therefore,the potato plants under R delayed leaf senescence,continued to supply photosynthates for potato-seeds,and prolonged biomass accumulation of potato-seeds.Potato-seeds under R up-regulated expression of APL2 to increase starch synthesis compared with other treamtents at 80 d.The potato-seed yield per plant under R was significantly higher than other treatments.The RW treatments(red light,200 μmol m-2 s-1;white light,100μmol m-2s-1)prolonged the accumulation of biomass in potato seeds at the later stage of plant growth.2.To analyze the physiological mechanism of red and blue light regulating the photosynthate distribution in potato plantsThe potato plantlets were transplanted under white light(W)for 30 days(0-30 d).During the tuber development stage(30-90 d),plants were transposed into white light(W→W)and red light(W→R),blue light(W→B)and 50%red+50%blue light(W→RB).W→R treatment had larger photo synthetic leaf area,stronger source activity and higher carbon assimilation compared with other treatments at 50 d.The higher the isotopic abundance(δ13C)value in plant organs,the more 13C assimilation the plant allocates to this organ.The isotope tracing experiment showed that the δ13C values in leaves under W→R were significantly higher than those of other treatments.Compared with W→W and W→B treatments,the stems and roots under W→R had significantly higher δ13C values,and they had no significant difference with W→RB.There was no significant difference for the δ13C values of potato-seeds per plant among W→R,W→ and W→RB,which was higher than that under W→W.The first potato-seed per plant developed earlier,had a longer growing period and accumulated more biomass than the second and third poato-seeds per plant.The δ13C value in the first potato-seed under W→R was significantly higher than those under other treatments,and the value was significantly higher than that of the second potato-seed per plant.Plants under W→R up-regulated the expression of SuSy4 and APL2 and increased starch biosynthesis in the first potato-seed per plant.The result showed that plants under W→R distributed more 13C assimilation into the first potato-seed per plant compared with the second potato-seed.Plants under W→R had a higher ratio of large potato-seeds(>20 g)and a lower ratio of small(2-20 g)and medium-sized(10-20 g)potato-seeds than those under W→W.The δ13C value in first potato-seed per plant under N→RB Was significantly lower than that under W→R,and was significantly higher than that under W→B.The δ13C value in second potato-seed per plant under W→RB was the highest among all treatments.The results showed that W→RB treatment was active on the biomass accumulation of two potato-seeds per plant.In W→RB treatment,the distribution ratio of large potato-seeds was between W→R and W→B treatments.The plants under W→B had significantly lower δ13C value and up-regulated expression of potato sucrose transporter 4 encoding gene(StSUT4)to inhibited biomass accumulation in the first potato-seed per plant compared with W→R.The plants under W→B had significantly higher δ13C value than those under W→R,thus promoting assimilation in the second potato-seed per plant.This result took advantage of achieving a balanced distribution of photosynthetic products of two potato-seeds per plant.The distribution ratio of medium-sized and large-sized potato-seeds under W→B was 41.2%and 43.3%,respectively.3.To show the difference effects of red and blue light regulating potato leaf growthThe 20-day-old potato leaves(L20d)was cultivated for 12 days under different spectral treatments on two pieces of filter paper soaked in distilled water in a petri dish.The results indicated that the chlorophyll content of leaves(L20d)under blue light(B)was significantly higher that under white light(W)and red light(R)treatments.The malondialdehyde(MDA)content of leaves(L20d)under B was significantly lower than that under other treatments.The 45-day-old potato leaves(L45d)were in vitro culture and the same spectral treatments.Leaves(L45d)under R delayed the senescence.The chlorophyll content in leaves(L45d)under R had no significant difference with B treatments,whereas The chlorophyll content in leaves(L45d)under R was significantly higher than that of W,B→R(B for 0-6 days→ R for 6-12 days)and R→B(R for 0-6 days→B for 6-12 days)treatments.The ascorbate peroxidase(APX)activity of R treated leaves(L45d)was significantly higher than those of other treatments,and its MDA content was significantly lower than that of B→R and R→B treatments.The leaves(L20d)had stronger ability to adapt to light environment comared with leaves(L45d)under B→R and R→B.The leaves(L20d)had no significant difference for the chlorophyll content among B,B→R and R→B.The peroxidase(POD)activity in leaves(L20d)was increased under B→R and R→B treatments.There were different ways to regulate leaf growth between combination of spectra and monochromatic spectrum.In summary,the red and blue light can affect poato-seed yield by regulating the biomass accumulation,photosynthate distribution and leaf growth.The red light promotes the carbon assimilation of potato plants and delays leaf senescence in the later growth period,thereby increasing the photosynthate accumulation and potato-seed yield per plant.Meanwhile,red light tends to distribute photosynthates to the first potato-seed per plant,which promotes a higher distribution ratio of large-sized potato-seeds.Blue light improved the photosynthetic pigment content and antioxidant capacity in potato leaves(L20d).Blue light accelertated biomass accumulation of potato-seeds by promoting the metabolism of sucrose and starch during the middle stage of potato-seed bulking.Potato plants under blue light balanced the photosynthate distribution among poato-seeds per plant.The combination of red and blue light was beneficial to shorten the potato-seed cultivation cycle,which can improve cultivation efficiency of potato-seeds.