Plant Growth Regulation

, Volume 36, Issue 2, pp 97–104 | Cite as

Phytohormone-mediated transformation of sugars to starch in relation to the activities of amylases, sucrose-metabolising enzymes in sorghum grain

  • Surekha Bhatia
  • Rangil SinghEmail author


Indole-acetic acid (IAA) and abscisic acid (ABA) were fed throughcomplete liquid medium (containing 2, 4, 8% sucrose) to detached earheads of sorghum. The effect of these phytohormones on interconvertion ofsugarsand their transformation to starch in relation to the activities ofα-, β-amylases, sucrose-synthase (synthesis), sucrose-phosphatesynthase and soluble invertases was studied in the grain. This effect on theuptake of (U-14C) sucrose by detached ear heads and incorporation of14C into free sugars and starch of grain and into free sugars ofinflorescence parts was also studied. At concentrations of up to 4%sucrose in the culture medium, IAA increased the content of total free sugarsinthe grain. However, accumulation of starch and activities of α- andβ-amylases increased when lAA was present even beyond the 4%sucroseconcentration in the culture medium. At all sucrose concentrations, the effectsof ABA and IAA were opposite. With 4% sucrose, both phytohormones causedmaximum accumulation of starch in the grain. ABA enhanced the relativeproportion of sucrose in the sugar pool with a concomitant reduction in theactivities of soluble acid (pH 4.8) and neutral (pH 7.5) invertases. Incontrast, IAA decreased the sucrose proportion of grain sugars with asimultaneous elevation and reduction in the activities of invertases andsucrose-phosphate synthase, respectively. Irrespective of sucrose concentrationin the culture medium, the activity of sucrose synthase (synthesis) wasenhancedwith IAA as well as ABA at their 10 μM concentration. IAA alsoenhanced incorporation of 14C from (U-14C) sucrose intothe EtOH extract (principally constituted by free sugars) and starch of thegrain, but ABA caused the reverse effect. Based on the results, it is suggestedthat IAA and ABA have contrasting effects on the transformation of sucrose tostarch in sorghum grain where its capacity to synthesise starch is modulatedpositively by IAA and negatively by ABA.

ABA Ear head culturing Grain IAA Invertases Starch hydrolyzing enzymes Sucrose synthase Sucrose-phosphate synthase 


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Copyright information

© Kluwer Academic Publishers 2002

Authors and Affiliations

  1. 1.Department of BiochemistryPunjab Agricultural UniversityLudhianaIndia

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