Histological and biochemical changes in Pinus spp. seeds during germination and post-germinative growth: triacylglycerol distribution and catalase activity

The spatio-temporal evolution of catalase (CAT) activity and triacylglycerol distribution was investigated in seeds and seedlings from Pinus pinaster Ait., P. pinea L. and P. radiata D. Don during germination and post-germination. The high amount of triacylglycerols contained in the whole dehydrated embryo from the three species was progressively depleted, first, in the radicle and then in hypocotyl and cotyledons during post-germinative growth. In parallel, histological localisation of CAT activity and the quantitative analysis confirmed the involvement of this enzyme in cell detoxification from peroxide released during the intense lipid breakdown. Two isozymes, CAT-1 and CAT-2, were identified during post-germinative growth. Both were particularly active in the hypocotyl and radicle, while CAT-2 was specifically active in the photosynthetic tissues. These results emphasise that CAT activity is also independent from lipid metabolism in certain tissues. The role of each isoenzyme is discussed in connection with the metabolic changes occurring during seed germination and seedling growth. Special attention is given to the role of the shoot apex in triacylglycerol storage and breakdown. Central mother cells have been shown as a specific lipid storage area of the shoot apical meristem, in contrast with the peripheral zone in which lipid reserves were always reduced.