The Coordination of Organ Growth in Developing Citrus Flowers: A Possibility for Sink Type Regulation

The interrelationships between simultaneously developing organsof citrus flowers were investigated. Examination of flower organgrowth kinetics shows that petals grow mainly through enhancedwater absorption whereas ovaries accumulate a high percentageof dry matter. Using excised flowers implanted in an agar—sucrose mediumand supplied with [¹⁴C]-sucrose, [³H]-acetate, and [¹⁴C]-acetate,a characteristic distribution of label among organs could beestablished for each isotope. Wounding or application of -naphthaleneacetic acid (NAA) toa single petal completely changed the normal distribution patterns,shifting the bulk of [¹⁴C]-sucrose towards the treated organs. The findings are interpreted in the light of the ‘sink’hypothesis. It is proposed that each flower organ meristem createsa sink of its own which acts in a typical manner according toits specific endogenous hormonal balance. The sink activityof all meristems in concert results in a sensitive regulatorymechanism which is responsible for the coordination observedin flower development.     

Uptake of 14C-gibberellic acid by mature grapefruit (Citrus paradisi Macf.) as affected by relative humidity and method of application

Effects of the method of application and relative humidity on the uptake of ¹⁴C-gibberellic acid (¹⁴C-GA₃) by mature grapefruit (Citrus paradisi Macf.) were examined. Uptake was higher when ¹⁴C-GA₃ was applied as a 'drying-out' solution than as a 'non-drying' solution. When ¹⁴C-GA, was applied by the 'drying-out' method, which closely imitates field conditions, rates of uptake were very high while the solution was drying out and during the first few hours after drying. Uptake from the dry residue continued in decreasing rates till the end of the experiment (72 h). Uptake from the dry residue was higher when fruits were incubated at 100% than at 50% relative humidity (RH). Transfer of fruits from 50% to 100% RH as late as 48 h after drying still increased the rate of uptake. Drying-out treatment solutions produced higher uptake rates with neutral (pH 7) as well as acid (pH 4) treatment solutions, and in the presence of triton B-1956, Triton X-100 or L-77 surfactants.     

BIOSENSORS: BLESSING OR BANE?

Biosensor technology is changing the methodology used to detect or characterize many microorganisms and/or their metabolites of importance to food microbiologists and the food industry. Biosensors have been developed to monitor the freshness of meat and fish. ATP and glucose concentrations have been monitored as well as continuous control operations in food processing. Enzyme-substrate transformations, DNA or RNA hybridizations and antibody-antigen interactions are examples of the types of molecules used in biosensor systems. Instrumentation coupled to the biological molecules and measuring the changes that occur include reactions on simple ion-sensing electrodes, as well as complex chips, optical fibers or piezoelectric crystals. In most cases, data can be obtained within a few minutes on very small amounts of compounds. However, the long term stability of the biological molecules involved in these procedures presents a major stumbling block. Partially or completely disposable devices are under consideration.