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  • Author or Editor: Wayne H. Loescher x
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Diurnal fluctuations in soluble carbohydrates and starch were monitored in young (expanding), mature (first fully expanded), and old (nearing senescence) celery (Apium graveolens L.) leaves. In all tissues, mannitol and sucrose were the carbohydrates present in the highest concentrations. In old and young leaflets and their petioles, there was little change in levels of mannitol and sucrose in 26 hours. In mature leaflets, sucrose accumulated in the light and decreased in the dark; mannitol increased slightly in late afternoon. Starch concentration, although quite low, showed definite diurnal fluctuations in mature leaflets, but only small changes in young and old leaflets. Both sucrose and mannitol were present in mature petiole phloem tissues. Mannitol concentrations were high in the adjacent storage parenchyma tissue, but sucrose was almost undetectable. These data support earlier findings that sucrose is produced, translocated, and metabolized throughout the celery plant. Mannitol is also translocated, but also serves as a major storage carbohydrate in leaf tissues, especially petiole parenchyma. Starch serves as a minor short-term storage compound in leaflets.

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Abstract

Relationships between leaf area per fruit and fruit weight, color, and soluble solids were modeled on spurs isolated following pit hardening on 2-year-old wood of ‘Bing’ sweet cherry (Prunus avium L.). Leaf area per fruit was found to be the largest measured source of variability in the three fruit quality parameters examined. Leaf area per fruit accounted for 66%, 36%, and 53% of the variability in fruit weight, fruit color, and soluble solids, respectively, at Pullman, Wash. Leaf area per spur accounted for 54%, 27%, and 28% of these same fruit quality parameters at Prosser, Wash. In all instances, there was a positive correlation between fruit quality and leaf area per fruit. Soluble solids content was most sensitive to increases in leaf area, followed by fruit weight and color. Leaf area per fruit is important because it represents photosynthetic potential. Ample productive leaf area is essential to producing high-quality sweet cherries.

Open Access

Mannitol, which in celery is a primary photosynthetic product, has been implicated along with other polyols in stress tolerance mechanisms as a possible osmotic regulator, compatible solute and free radical scavenger. We have characterized the growth of salt stressed celery, determined the extent of salt tolerance and showed a correlation between mannitol accumulation and salt tolerance.

Six, 8 and 12 week-old pot grown celery (Apium graveolens L.) plants of two cultivars were irrigated with up to 500 mM NaCl for 3.5 and 7 weeks. After 7 weeks, 12 week-old `Giant Pascal' plants showed three major responses: 1) shoot wet wt increased as much as 30% at 25 mM NaCl but root wet wt decreased; 2) plants tolerated 500 mM NaCl, although at a severely reduced growth rate; 3) as salt concentrations increased mannitol concentrations increased in roots, leaves and petioles, while sucrose, the other photosynthetic product in celery, decreased Although all ages of both cultivars tolerated the highest salt concentration used, the beneficial effect of 25 mM NaCl occurred only in 8 and 12 week-old `Giant Pascal'. Root wet wt was reduced in all salt treated plants, irrespective of age or cultivar.

Regardless of age, cultivar and length of treatment, celery tolerated high salinity and sometimes even increased wet wt at low salinity. Mannitol accumulation and the ratio of mannitol to sucrose were both positively correlated with salt tolerance

Free access

Abstract

The rate and efficiency of photosynthesis (PS) is unquestionably one of the primary determinants of crop yield. Yet, as this symposium illustrates, many other factors contribute to plant productivity. Indeed, the exact relationship between PS rate and yield remains undefined. For several years we have now been interested in factors that affect PS rate in both C3 and C4 plants, not only within the plant, but also external to it. Internal factors affecting PS that will be discussed include leaf age, leaf canopy, photorespiration, stage of plant development (including both vegetative and reproductive phases), and the occurrence of little-recognized metabolic pathways such as polyol synthesis and transport. External factors that affect PS, in addition to obvious environmental determinants such as temperature, light, and water, include the seasonal growth cycle. While we still do not understand how all of these factors interact to affect yield, we are beginning to understand their singular effects. Control of these factors, once thought to be within reach even before the advent of biotechnology, remains likely, but distant.

Open Access

Mannitol, a sugar alcohol that appears to serve as an osmoprotectant/compatible solute to cope with salt stress, is synthesized in celery (Apium graveolens L.) via the action of a NADPH dependent mannose-6-phosphate reductase (M6PR). To evaluate the abiotic stress effects of mannitol biosynthesis, we transformed celery with an antisense construct of the celery leaf M6PR gene under control of the CaMV 35S promoter. Unlike wild type (WT) celery, independent antisense M6PR transformants did not accumulate significant amounts of mannitol in any tissue, with or without salt stress. In the absence of NaCl, and despite the lack of any significant accumulation of mannitol that is normally the major photosynthetic product, antisense transformants were mostly phenotypically similar to the WT celery. However, in the presence of NaCl, mature antisense transgenic plants were significantly less salt-tolerant, with reduced growth and photosynthetic rates, and some transformant lines were killed at 200 mM NaCl, a concentration that WT celery can normally withstand. Although mannitol biosynthesis is normally enhanced in salt-treated WT celery, no such increase was observed in the antisense transformants. Like our previous gain of function results showing enhanced salt tolerance in Arabidopsis plants transgenic for a sense M6PR construct, these loss of function results, using an antisense construct in celery, demonstrate a major role for mannitol biosynthesis in developing salt-tolerant plants.

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