Accumulation of several low-molecular-weight solutes was measured in the developing floral apex, in an enclosed, elongating leaf, and in an expanded leaf of wheat plants during a 13-day period of water stress. In the apices and enclosed leaves, osmotic potential fell from - 1.2 to -4.0 MPa. The main contribution to the decline in osmotic potential during the first 3 days of stress was from an increase in the content of ethanol-soluble carbohydrate. Later, increases in the concentrations of both carbohydrates and amino acids made major contributions. Of the amino acids, the largest increases were in asparagine and proline. The enclosed tissues lost little water, although the water- to-dry matter ratio declined as a result of imported solutes. The ethanol-insoluble nitrogen content of apices remained high, and growth of apices and enclosed leaves recommenced when plants were watered after 13 days. In exposed leaves, increases in carbohydrate and amino acid contents were comparatively small, and the content of ethanol-insoluble nitrogen decreased by 50%. These leaves dehydrated within 6 days, and failed to recover when the plants were rewatered.
Endopolygalacturonase [poly(1,4-α-D-galacturonide) glycanohydrolase, EC 3.2.1.15] was purified from ripening tomato fruits. The dominant enzyme in fruits at an early stage of ripening had a native molecular weight (Mr) of about 115 000, an isoelectric point (pI) of 8.6, and retained 50% of activity after 10 min at 70°C. Divalent metal ions enhanced the activity of this enzyme and ethylenediaminetetraacetate (EDTA) inhibited activity. In fully ripe fruits, two enzymes of Mr about 43 000 and 46 000 were most prominent. These enzymes each had a pI of 9.4; when a mixture of these two enzymes was heated for 10 min at 50°C, 50% of activity was lost. Antibodies raised against the smallest enzyme, Mr 43 000, reacted also with the larger enzymes. After denaturation in sodium dodecyl sulfate, the largest (Mr 115 000) and smallest (Mr 43 000) enzymes yielded polypeptides of identical size while the third enzyme (Mr 46 000) was slightly larger. All three enzymes were glycoproteins. From fully ripe fruits, enzyme preparations with specific activities of 1.7 �kat mg-1 were obtained. This specific activity exceeds those described previously for plant polygalacturonases.
Endopolygalacturonase (EC 3.2.1.15) activity, endopolygalacturonase protein detected immunologically and water-soluble uronide were measured in tomato fruit samples (cv. Rutgers) at different stages of ripening. Endopolygalacturonase activity and endopolygalacturonase protein were only detected in samples in which ripening had been initiated for 2 or more days. Enzyme activity and enzyme protein increased during ripening and were highly correlated. A high molecular weight form of the enzyme appeared 2 or 3 days after ripening was initiated. Lower molecular weight forms of endopolygalacturonase appeared later and eventually accounted for most of the enzyme protein. The content of water-soluble uronide did not increase until fruit had been ripening for 4 or more days. It is concluded that endopolygalacturonase is not involved in the initiation of ripening.
The pectinesterase (pectin pectyl-hydrolase, EC 3.1.1.11) of the pulp of the banana fruit is completely solubilized by buffers containing 0.5M sodium acetate, and the activity of the enzyme in the pulp remains constant during ripening. An apparent change in the ease of extraction as ripening progresses may be artefactual. The enzyme has been purified 200-fold from climacteric fruit. In either case, a molecular weight about 30 000 is indicated by chromatography through Sephadex G200. After isoelectric focusing, the enzyme was found in two peaks, at pH 8.8 - 8.9 and at pH 9.3 - 9.4. The enzyme in the two peaks is of the same molecular size, and shows only minor differences in responses to pH, salt and polyol concentration during assay. These results are discussed in relation to previous publications concerning changes in pectinesterase activity and properties during ripening of banana fruits.
A pressure dehydration technique for recovering sap from the apoplast of the pericarp tissue of developing tomato fruit has recently been developed. Samples of this sap from two cultivars have now been analysed for sugars, amino acids, organic acids, ammonia and inorganic ions. The measured solutes accounted for 92 and 97% of the osmolality of the apoplast sap from the two cultivars. The osmotic potential of the apoplast samples was similar in the two cultivars, and the apoplast samples were distinctly different in osmolality and in composition from samples of the bulk sap obtained after thawing frozen tissue. Hexoses and inorganic compounds, principally potassium and chloride, accounted for 75% of the osmotic potential of the apoplast samples. There is little prior information on the composition of the apoplast in fruit. The impact of this new knowledge is discussed in relation to the uptake of solutes into fruit cells, the partitioning of solutes between apoplast and symplast, and the ionic environment of the cell wall and wall-bound enzymes.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.