03050nam a2200253 a 450000100080000000500110000800800410001910000170006024501680007726000500024530000100029550000340030552022870033965000180262665000210264465000210266565000160268665000150270265000170271765000200273465000100275465300170276465300150278115594301999-11-23       1985    bl uuuu  m   00u1 u    #d1 aCOSTA, S. P.  aPhysiological and anatomical factors enfluencing the pattern of carbohydrate accumulation in senescent and nonsescent sorghum (Sorghum bicolor (L.) Moench) plants.  a[College Station]: Texas A&M Universityc1985  a147p.  aDoctors of Philosophy Thesis.  aTwo sorghum cultivars, ATx378 x RTx430[(34), higher stem carbohydrates and slower rate of senescencel] and ATx378 x RTx7000 [(37), lower stem carbohydrates and more rapid rate of senescencel] were utilized in a stydy of factors to determine possible anatomical and physiological differences. Plant spacings of 10 or 40 cm four within the rows, were used. Evaluations were performed at four selected matutiry stages: (PB), 15 days post anthesis (PA), layer (PBL). Cultivar 34 had approximateley 45% of the bundle-sheath cell volume filled with chloroplasts, 2 - 3 - 3 mesophyll cells between veins and a shorter distance between veins. By contrast, cultivar 37 contained only 19% of the bundle-sheath cell volume filled with chloroplasts, 3 - 4 mespphyll cells between veins and a larger distance between veins. Stems of closer spaced plants contained more but smaller vascular bundles than wider spaced ones. Phoem vessels of cultivar 34 coveres 23% of the total vascular bundle area, whereas only 18% was covered for 37. Cultivar 34 produced the highest carbon dioxide assimilation rates. PEP carboxylase enzyme activity, measured in the crude extract of the flag leaf, and the assimilation rates, descresead in a stepwise trend as plant maturity progresses. Cultivar 34 produced significantly higher stem nonstructural carbohydrates (NSC) for all fractions determined. Closes spaced plants contained significantly higher levels of sucrose and total  NSC. The lowest concentration for all carbohydrate franctions, except glicose, generally ocurred at PA, which coincided with maximum panicle growth and kernel filling. After completion of kernel filling, carbohydrates were again accumulated in the stem. Starch was present in higher levels at the earlier, decresead a PA and incresead again at later stages, but at higher concentrations for the slower senesing than for the faster senescing cultivar. Higher carbohydrate accumulation of the cultivar 34 was evidently enhanced by the leaf characteristics. This is indicated by a larger volume of bundle-sheath cell chloroplasts, higher density of mesophyll chloroplasts, and a shorter distance between veins. This, plus a larger area of phoem vessels in the stem vascular bundles should result in a more efficient transport system.  aplant anatomy  aplant physiology  aAnatomia Vegetal  aCarboidrato  aFisiologia  aSenescência  aSorghum Bicolor  aSorgo  aCarbohydrate  aSenescence