Pyrophosphatase, Peroxidase and Polyphenoloxidase Activities during Leaf Development and Senescence

Abstract

Inorganic pyrophosphatase, peroxidase, and polyphenoloxidase activities were studied as the function of leaf insertion level in eight monocotyledonous and eight dicotyledonous species. Alkaline inorganic pyrophosphatase shows a declining activity toward the end of senescence whereas no regular drift in either peroxidase or polyphenoloxidase activities was noticed during senescence of attached leaves. In the primary leaves of rice, peroxidase and polyphenoloxidase activities were high in the senescent leaves and there exists a correlation between chlorophyll content and peroxidase activity though not with polyphenoloxidase activity. Upon detachment leaves exhibit increasing peroxidase and polyphenoloxidase activities with time. The distribution of the enzyme activities during senescence of attached leaves is suggested to be species-specific, and an increase in peroxidase and polyphenoloxidase activities cannot be taken as an indicator of leaf senescence.A number of reports are available regarding the increase (1, 2, 4, 7-10, 14, 16, 19) and/or decrease (4,10,12,19,20) in activities of several hydrolyzing and oxidative enzymes during senescence of leaves. Differences in the senescence pattern of attached leaves compared to detached leaves or leaf discs have been reported (13,14,24, 25).Both acid and alkaline inorganic pyrophosphatase (EC 3.6.1.1) occur in higher plants (17). It has been suggested that the alkaline inorganic pyrophosphatase, having extremely high affinity for pyrophosphate, is associated with the anabolic process in the leaf, while acid inorganic pyrophosphatase participates in the catabolic process (7,21,23 This investigation was undertaken to study the distribution pattern of inorganic pyrophosphatase, peroxidase, and polyphenoloxidase activities in attached leaves of different physiological ages and to determine if the changes in peroxidase and polyphenoloxidase activities during leaf senescence can be considered to be species-specific. MATERIALS AND METHODSThe following species were investigated: monocotyledons: Amomum aromaticum Roxb., Eleusine corocana Gaertn., Hordeum vulgare L., Oryza sativa L., Pennisetum typhoideum Rich., Sorghum vulgare Pers., Triticum vulgare Villars., and Zea mays L.; dicotyledons: Arachis hypogaea L., Boerhaavia diffusa L., Chenopodium album L., Crotolaria striata DC., Hibiscus micranthus L., Nicotiana plumbaginifolia Viv., Raphanus sativus L., and Tabernaemontana coronaria Br.Healthy plant samples were collected on sunny days at 10 AM and the approximate age of the organs determined by the method of Kornilov et al. (11). The samples were transported to the laboratory in polyethylene bags covered with crushed ice. The leaves were numbered from the apex downward so as to obtain subsamples representative of various developmental stages. The leaves were excised within 15 min of collection, washed thoroughly with tap water, and then in distilled H20. The leaves were blotted, weighed, and stored in a refrigerator at 8 C for 30 min.Enzyme Extraction and Assay. Enz...

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