| Many processes take place during leaf development of tall fescue ( Festuca arundinacea Schreb.). Epidermal cells divide at 0 to 5 mm from the ligule, then expand up to 30 mm. Carbohydrate (CHO) storage and CHO utilization take place at 0 to 30 and 30 to 70 mm, respectively, above the ligule. Insoluble nitrogen (N) and total N are deposited at 0 to 20 mm. However, where in the meristem and leaf growth zone that photosynthetic competency develops is not clear. My objectives were to determine how and where stomata, mesophyll tissue, and chloroplasts develop as leaf cells form in tall fescue, to study how genotype and N level affect cellular formation processes, and to develop an understanding of the spatial and temporal framework for development of photosynthetic competency during growth of grass leaves.; Based on photosynthesis data obtained in a greenhouse, the photosynthetic rate per unit leaf area (A) increases as ploidy level increases. The A of F. mairei St. Yves, a tetraploid, is 25.1 mumol m-2 s-1, about 30% higher than that of a hexaploid genotype (HYT) of F. arundinacea. Based on analyses using electron and light microscopy, development of the stomatal complex in the HYT genotype (rapid leaf growth rate) starts about 3 mm from the leaf ligule. Guard mother cells, subsidiary cells, and guard cells form at 4 to 6, 6 to 9, and 9 to 10 mm, respectively. The stomatal aperture opens at 15 mm, then closes again at 29 to 30 mm. Mesophyll cell division occurs at 1 to 15 mm above the ligule followed by mesophyll cell enlargement from 10 to 15 mm. The airspaces form at 8 to 29 mm, mainly between 15 and 29 mm.; Number of chloroplasts (proplastids) per mesophyll cell is very high (about 250 per cell) at the base of the leaf blade, then declines rapidly as mesophyll cells divide. At 10 mm, there are about 40 chloroplasts per mesophyll cell after which number of chloroplasts increases to about 110 per cell at 50 mm. Chloroplast volume increases about 20-fold from the leaf base to 100 mm. Chloroplasts also increase in granum number up to 17 and in thylakoid layers up to 16 in mature leaves. Chlorophyll biosynthesis is rapid at 50 to 150 mm.; These data show development of stomatal factors, such as stomata and airspaces, occurs earlier than development of non-stomatal factors, such as chloroplasts and chlorophyll, regulating photosynthesis. |
