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School of Biological Sciences

The University of Hong Kong

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Dr. W. K. Yip

Research Area


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Tomato


  1. Physiology and molecular biology of plant hormone ethylene
  2. Plant hormone ethylene regulates many aspects of plant growth and development, including seed germination, fruit ripening, flower fading, leaf senesence and abscission. Manipulation of the levels of ethylene in plants, either by increasing or decreasing ethylene production rates, is an useful option applicable to the optimization of many agricultural systems. 1-aminocyclopropane-1- carboxylate (ACC) synthase and ACC oxidase are two important enzymes that regulate ethylene biosynthesis in plant tissues. The cloning of ACC synthase and ACC oxidase genes is essential to obtain further information about the mechanism and regulation of ethylene biosynthesis which can be used to establish a theoretical basis from which ethylene production by crops plants and its physiological consequences can be regulated via biotechnology. Many of my present projects related to ethylene biosynthesis are funded by the RGC (Research Grant Council), Croucher Foundation and the CRCG (Committee on Research and Conference Grants) in the University of Hong Kong.

  3. Signal transduction in plants
  4. Plant growth and metabolism can be rapidly controlled by stimuli such as light, hormones and environmental stresses. These responses may not be involved in the transcription level, but rather through the modification of existing enzymes/proteins. It appears likely that, as in animal cells, reversible phosphorylation of plant proteins is central in the transduction of excellular signals into intracellular biochemical events. However, only a few enzymes in plant cells have been demonstrated to be regulated by this phosphorylation/dephosphorylation reactions. AMP-activated protein kinase regulates key enzymes of mammalian fatty acid sterol and isoprenoid metabolism, including 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase. Recently MacKintosh et al (1992) and Ball et al (1994) discovered that there is an enzyme activity in higher plants (cauliflower, tomato etc.) which, by functional criteria, is a homologue of the AMP-activated protein kinase, although it is not regulated by AMP. Their results also indicated that plant HMG-CoA reductase would be inactivated after phosphorylated by this kinase activity. HMG-CoA reductase catalyses the reduction of HMG-CoA reductase would be inactivated after phosphorylation by this kinase activity. HMG-CoA reductase catalyses the reduction of HMG-CoA to mevalonic acid, the committed step in isoprenoid biosynthesis. Since this committed step is also rate limiting the properties and regulation of the enzyme are pertinent to the biosynthesis of most of the multitude of primary and secondary isopentenoids synthesized in plants, including phytoalexins, pigments, rubber etc. These discoveries prompt us to further investigate on this protein kinase activity in plants because this will lead us to understand how the synthesis of these important metabolites are being controlled in plants. My present projects on these aspects are:
    (a) Purification of the HMG-CoA reductase to homogeneity;
    (b) Structural determination of HMG-CoA reductase kinase;
    (c) Determination of the regulatory features in HMG-CoA reductase by HMG-CoA reductase kinase as substrate specificity determinants and
    (e) Elucidation of the regulatory mechanisms of the HMG-CoA reductase kinase.

  5. Postharvest storage and handling of Lychee
  6. (Co-PI: Dr Y.B. Ho)

    Lychee is considered as a local fruit which originated in China's Kwantung Province. The fruit consists of a white to cream-colored translucent pulp which is the edible part, one seed and a red scarly peel. The pulp is grape-like in texture, very succulent, and aromatic and is characterized by sweet and acid tastes. It is one of the popular fruit in Hong Kong. During the summer, the fruiting season lasts for about 2 months. Unfortunately, lychee is a minor fruit crop, little postharvest research has been done on this commodity. The reports on the postharvest physiology and the postharvest losses of lychee are scanty. The shelf life of fresh unpackage lychee at room temperature is less than 3 days. Desiccation occurs during transport with accompanied loss of red shell color and development of browning due to the polyphenol oxidases in the peel. When the peel turns brown, the fresh favor also degenerates.

    With the physical closeness of the lychee plantation, we have initiated a systematic study on the postharvest physiology and postharvest handling of this fruit crop. We aim at the possibility of extending the shelf life of lychee, finding a way to store it for a longer period (1 to 3 months) without losing its fresh favor, preventing the browning of the red shell and thereby reduce the spoilage.


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