葉綠素

葉綠素jip6 luk6 sou3（英文：chlorophyll）係植物同藻入面嘅綠色色素，負責做光合作用。

消耗

葉綠素可以隨時間而消耗：葉綠素幫植物吸收太陽光，用陽光中嘅能量，由水（H₂O）同二氧化碳（CO₂）呢啲原材料嗰度製造糖份俾樖植物用嚟做嘢食，而呢啲糖份會為植物提供佢哋生長同發育所需嘅所有碳水化合物；喺呢過程當中，葉綠素會受到分解－光合作用會消耗葉綠素。不過喺生長季節，植物能夠補充流失咗嘅葉綠素^[1]，令到啲葉保持綠色^[2]。

分解

夏天結束所伴隨嘅環境變化會令到葉嘅葉綠素含量下跌：喺夏天就快結束嗰陣，日頭會變短，溫度會跌，葉上面嘅葉脈（喺維管束植物嘅葉當中負責運送水份同營養嘅管道）會慢慢噉收細，於是塊葉嘅水份同礦物質吸收會慢慢噉下跌，而隨住葉綠素嘅消耗同時葉綠素嘅吸收跌，葉綠素嘅含量亦都會開始跌^[2]。

紅葉嘅出現同捕光複合物 II（light-harvesting complex II，LHC II）好有關。LHC II 喺光合作用當中負責吸收陽光，位於葉綠體嘅類囊體（thylakoid）膜嗰度，由多種蛋白質（包括咗葉綠素 a 同 b）組成；喺秋天嗰時，分解葉綠素嘅酵素會令到葉綠素 b 變成葉綠素 a ^[3]；呢個過程會造成捕光複合物變得唔穩定，最後搞到組成 LHC II 嘅某啲蛋白質分解，最後引致葉入面嘅葉綠素量急跌^[4]。

葉綠素嘅分解最後嘅結果係葉會變色。隨住葉綠素分解，葉綠素會變成冇顏色嘅化合物四吡咯（tetrapyrroles），而隨住綠色量下跌，葉入面本嚟有嘅第啲色素，好似係黃色嘅葉黃素類（xanthophylls）同橙色嘅 β-胡蘿蔔素（beta-carotene）嘅顏色會開始顯眼，而且喺某啲情況下，一半嘅葉綠素分解咗之後，紅色嘅花色素苷（anthocyanins）會開始產生^[5]；同時樖植物會將捕光複合物分解所產生嘅氨基酸儲起喺根、枝、同幹嗰度，用嚟喺冬天用，而下年就可能攞呢啲氨基酸嚟重整綠葉^[6]。

睇埋

攷

↑ Smith, L. W. (1944). Chlorophyll: An experimental study of its water-soluble derivatives: IV. The effect of water-soluble chlorophyll derivatives and other agents upon the growth of fibroblasts in tissue culture. The Journal of Laboratory and Clinical Medicine, 29(3), 241-246.
↑ ^2.0 ^2.1 Matile, P. (2000). Biochemistry of Indian summer: physiology of autumnal leaf coloration. Experimental gerontology, 35(2), 145-158.
↑ Horie, Y.; Ito, H.; Kusaba, M.; Tanaka, R.; Tanaka, A. (2009). "Participation of Chlorophyll b Reductase in the Initial Step of the Degradation of Light-harvesting Chlorophyll a/b-Protein Complexes in Arabidopsis". Journal of Biological Chemistry. 284 (26): 17449–56.
↑ Zelisko, A.; Garcia-Lorenzo, M.; Jackowski, G.; Jansson, S.; Funk, C. (2005). "AtFtsH6 is involved in the degradation of the light-harvesting complex II during high-light acclimation and senescence". Proceedings of the National Academy of Sciences. 102 (38): 13699–704.
↑ Hortensteiner, S. (2006). "Chlorophyll degradation during senescence". Annual Review of Plant Biology. 57: 55–77.
↑ Chapin III, F. S., Schulze, E. D., & Mooney, H. A. (1990). The ecology and economics of storage in plants. Annual review of ecology and systematics, 21(1), 423-447.

[1] Smith, L. W. (1944). Chlorophyll: An experimental study of its water-soluble derivatives: IV. The effect of water-soluble chlorophyll derivatives and other agents upon the growth of fibroblasts in tissue culture. The Journal of Laboratory and Clinical Medicine, 29(3), 241-246.

[matile2000-2] 2.0 ^2.1 Matile, P. (2000). Biochemistry of Indian summer: physiology of autumnal leaf coloration. Experimental gerontology, 35(2), 145-158.

[3] Horie, Y.; Ito, H.; Kusaba, M.; Tanaka, R.; Tanaka, A. (2009). "Participation of Chlorophyll b Reductase in the Initial Step of the Degradation of Light-harvesting Chlorophyll a/b-Protein Complexes in Arabidopsis". Journal of Biological Chemistry. 284 (26): 17449–56.

[4] Zelisko, A.; Garcia-Lorenzo, M.; Jackowski, G.; Jansson, S.; Funk, C. (2005). "AtFtsH6 is involved in the degradation of the light-harvesting complex II during high-light acclimation and senescence". Proceedings of the National Academy of Sciences. 102 (38): 13699–704.

[5] Hortensteiner, S. (2006). "Chlorophyll degradation during senescence". Annual Review of Plant Biology. 57: 55–77.

[6] Chapin III, F. S., Schulze, E. D., & Mooney, H. A. (1990). The ecology and economics of storage in plants. Annual review of ecology and systematics, 21(1), 423-447.

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