光質對水稻幼苗形態與光合生理之影響

本研究主要評估光質對於水稻幼苗之形態與光合生理之影響。先行探討幼苗生長、發育與碳、氮代謝方面對於不同光質之反應。水耕幼苗栽培於紅(R)、綠(G)、藍(B)與紅藍(RB)發光二極體(light-emitting diode, LED)照射之生長箱。紅光誘導地上部伸長。藍光抑制伸長並促進壯苗指數。相較於紅藍混和，葉片總蛋白在藍光照射下含量較高。另外光合生理方面，藍光可提高幼苗葉片之光系統II有效光量子產量(ΦPSII)與光化學消散(qP)，同時降低非光化學消散(NPQ)。水稻幼苗對紅光與綠光的反應相當類似。幼苗葉片花青素含量以RB最高，R、B卻低於G。葉片中葉綠素 a/b 比例則受不同光質波段所調控。　　另外結果顯示，不同光質對於光合作用與氮素代謝具不同效果，而此類生理反應與水分利用效率(water-use efficiency, WUE)、氮素吸收具相關性。進一步探討水稻在不同光質處理下，WUE、穩定性碳同位素分辨率(Δ13C)與氮素吸收反應，另以螢光燈(FL)為對照。發現R之幼苗WUE最高，而後依序為G、RB、B。除了FL處理之外，WUE與Δ13C具顯著正相關(P<0.01)。另利用氮含量與氮同位素值(δ15N)評估不同光質對於氮肥吸收之結果顯示，幼苗中化學肥貢獻之氮素(Nf)以B最高而R最低。因此，推測藍光可促進氣孔導度與蒸散作用，造成WUE降低而促進根部氮素吸收。　　在此水稻幼苗葉片之葉綠素(chlorophyll, Chl)與其生合成中間產物(protoporphyrin IX, PPIX; magnesium protoporphyrin IX, MGPP; protochlorophyllide, Pchlide)、降解代謝產物(chlorophyllide, Chlide; pheophytin, Phe; pheophorbide, Pho)以及胡蘿蔔素(carotenoid, Car)。葉片中Chl與Car在綠光下較低。光質並未影響生合成途徑中卟啉(porphyrins)莫爾百分比。Phe/Chlide在G與FL照明下數值較低，顯示綠光較高之環境會促進葉片中Chlilde分解途徑。　　為了釐清綠光在Chl分解途徑之效應，將幼苗在固定紅、藍光強度40 μmol m-2 s-1)下生長，分別以4個綠光等級(0, 20, 40 and 60 μmol m-2 s-1) 處理。同時調查部分形態與光合生理。結果顯示，在固定紅、藍光下隨著綠光強度增加，水稻幼苗具較長之葉鞘且葉片角度較為直立，具避蔭效應(shade avoidance symptoms, SAS)。且增強綠光亦會造成葉綠素、ФPSII降低與NPQ提高。另外增強綠光下，也發現較高之Chlide與較低之Phe/Chlide比例。以上結果顯示綠光可誘導水稻幼苗之SAS產生且調節Chl分解途徑。

關鍵字

水稻幼苗；光質；光形態發生；降解代謝；穩定性同位素；水分利用效率；氮素吸收；葉綠素分解途徑；避蔭效應

並列摘要

Our objective in this study was to evaluate the effect of light quality on the morphology and photosynthetic physiology of rice seedlings. We examined the growth, development, and metabolic responses of rice seedlings to varying light quality firstly. Seedlings were hydroponically cultured under red (R) light-emitting diodes (LED), green LED (G), blue LEDs (B), and red + blue LED (RB) inside growth chambers. Red light induced shoot elongation. B light inhibited shoot elongation and promoted health index values. B light also resulted in higher total protein content in tested leaves compared to RB. Blue light enhanced the effective quantum yield of PSII photochemistry (ΦPSII) and photochemical quenching (qP) while reducing non-photochemical quenching (NPQ) in seedling leaves. The responses of rice seedlings to green and red light were quite similar. The anthocyanin content of seedling leaves was observed to be highest in RB but less so in R and B, the latter two being even lower than in G. Different wavelengths mediated the chlorophyll (Chl) a/b ratio of the leaves. Light quality influenced photosynthetic potential and nitrogen metabolism, which are related to water-use efficiency (WUE) and nitrogen uptake. We further investigated the response of time-integrated WUE, 13C discrimination (Δ13C), and nitrogen uptake in hydroponic seedlings of rice grown under different light treatments with fluorescent light (FL) as the control. The WUE response was highest for seedlings grown under R light, then (in decreasing order) seedlings grown under G, RB, and B light. WUE had a significantly positive correlation with Δ13C except under FL light (P<0.01). Nitrogen content (%N) and δ15N values were used to estimate the effects of fertilizer uptake under different lighting conditions. The amount of N in seedlings derived from fertilizer (Nf) was highest under B light and lowest under R light. Therefore, we conclude that blue light may increase stomatal conductance and transpiration, decrease WUE, and promote root N uptake. The dynamics of Chl, biosynthetic intermediates (protoporphyrin IX, PPIX; magnesium protoporphyrin IX, MGPP; protochlorophyllide, Pchlide), degradation intermediates (chlorophyllide, Chlide; pheophytin, Phe; pheophorbide, Pho), and carotenoids (Car) in leaves of rice seedlings were also investigated. Lower levels of Chl and Car in leaves were observed under G lighting. Light quality did not mediate the mole percent of porphyrins in biosynthetic pathways. Lower Phe/Chlide ratios were observed under G and FL lighting conditions, indicating that green-enriched environments may up-regulate the Chlide degradation route in leaves. In order to clarify the effect of green light on the Chl degradation pathway, seedlings were grown under equal intensity (40 μmol m-2 s-1) of red and blue light with four levels of green light intensity (0, 20, 40, and 60 μmol m-2 s-1). Some morphological traits and photosynthetic physiology were also investigated at the same time. Sheaths of rice seedling leaves became elongated and leaves grew more erectly under red and blue light with increasing green light intensity. These morphological traits are known as shade avoidance symptoms (SAS). Lower Chl, decreasing ФPSII, and increasing NPQ were also observed under increasing green light intensity. Higher Chlide levels and lower Phe/Chlide ratios were observed under increases in green light intensity. These results indicated that green light induced SAS and mediated Chl degradation routes in rice seedlings.

並列關鍵字

Rice seedling ； Light quality ； Photomorphogensis ； Metabolism ； Stable isotope ； Water-use efficiency ； Nitrogen uptake ； Chlorophyll degradation pathway ； Shade avoidance symptoms

參考文獻

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光質對水稻幼苗形態與光合生理之影響

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