麦芒的结构及其光合特性

STRUCTURE AND PHOTOSYNTHETIC CHARACTERISTICS OF AWNS OF WHEAT AND BARLEY

小麦芒的横切面呈锐角三角形，而大麦芒呈钝角三角形。芒的二个侧面上具有成带状排列的气孔，气孔带下方为绿色组织。绿色细胞是由薄壁细胞分化来的，发育完全的绿色细胞具有突起，细胞间有很大的空隙。麦芒叶绿体的片层结构发达，内含淀粉粒，芒中有３条有限外韧型维管束，靠近绿色细胞的外鞘细胞中含有叶绿体。绿色细胞中的光合产物可能通过鞘细胞和伴胞进入筛管，麦芒的光合强度和开花期最高，可达２０μｍｏｌＣＯ２·ｍ＾－２·

The surface and the cross section of awns of wheat and barley were examined by scanning electron microscopy,ultrastructure of cells were observed under a transmisson electron microscope and the photosynthetic rates were measured with an oxygen,electrode and infra-red CO_2 analyser. The main results were as follows:The cross section of wheat awn appeared to be acutely trianglular whereas that of barley awn was obtusely triangular. There were rows of stomota on either side of epidermis in both wheat and barley awns. Under the stomatic band there were green tissues. The green cells in the awn were differentiated from the parenchyma cells . The mature green cells possessed papillae which were rich in chloroplasts and mitochondria. The lamella system in chloroplasts was well developed and contained many starch grains. There were three vascular bundles in each awn. The sheath cells near the green tissues contained chloroplasts. The photosynthate in the green cells might pass through the sheath cells and companion cells to sieve elements. The highest photosynthetic rate of the awn was seen at the flowering stage ,reaching about 20 μmol CO_2 • m^(-2) • s^(-1). The light compensation point was 70-80 μE • m^(-2) • s^(-1). The light saturation point was about 1500 μE • m^(-2) • s^(-1) The CO_2 compensation point was 50-60 ppm and the CO_2 saturation point was about 900ppm . The photosynthetic rate and stomatal conductance were easily effected by CO_2concentration, light intensity and the duration of illumination . There was a positive correlation between the photosynthetic rate and the chloro-phyll content in the awns. The CO_2-releas- ing rate in photorespiration of awn was about 4-5 μmol CO_2 • m^(-2) • s^(-1).