Folic acid and vitamin C were used in the concentration range of 0-500muM as exogenous growth enhancers to stimulate pea (Pisum sativum) seedling vigour. The results suggest that a concentration of 50muM folic acid and 500muM vitamin C were optimum in maximally enhancing seed vigour and potentially seedling performance according to both agronomic and biochemical seed vigour parameters. Results indicated that germination percentage, shoot weight, shoot height, and root length were enhanced in folic acid and vitamin C treated plants compared to control plants. The levels of enhanced phenolic content in response to folic acid and vitamin C treatments were highest on days 8 and 10. Evaluation of critical biochemical parameters indicated that the average glucose-6-phosphate dehydrogenase (G6PDH [?]) activity and proline content in response to treatments were higher than control and correlated to enhanced phenolic content and DPPH-based antioxidant activity. Key enzymes, guaiacol peroxidase (GPX), superoxide dismutase (SOD), and catalase (CAT) were also higher in response to treatments and correlated to enhanced phenolic content and DPPH-based antioxidant activity. Taken together, these studies support the hypothesis that the proline-linked pentose phosphate pathway stimulates phenolic synthesis and related free-radical scavenging antioxidant activity. Further, this proline-linked pentose phosphate pathway stimulation in response to folic acid and vitamin C was also correlated to antioxidant enzyme response indicated by the stimulation of GPX, SOD, and CAT activities. Therefore, this study indicates the enhancement of seed vigour response by folic acid and vitamin C as reflected in both agronomic and biochemical responses, and this occurred through the stimulation of phenolic-linked antioxidant response that is likely positively modulated through the proline-linked pentose phosphate pathway.
From Golden Harvest Organics "People aren't the only ones in need of antioxidants to neutralize free radicals. Scientists have long known that plants use their own vitamin C to reduce oxidative damage. Now, Agricultural Research Service scientists are looking into ways that plants use vitamin C to defend against ozone, which damages more plants than all other air pollutants combined.
Stratospheric, or upper-level, ozone protects Earth from harmful ultraviolet radiation. But tropospheric, or ground-level, ozone, is a pollutant. Tropospheric ozone results when air pollutants react with oxygen in the presence of sunlight to form a molecule with three highly charged oxygen atoms (O3). Tropospheric ozone enters plants through their leaves and decomposes into unstable molecules called reactive oxygen intermediates (ROIs). If not neutralized by an antioxidant, ROIs injure plants.
At the Air Quality-Plant Growth and Development Research Unit in Raleigh, North Carolina, plant physiologist Kent Burkey is studying how plants transport vitamin C out of their leaf cells and into a complex of adjoining cell walls. This outer cellular space is called the apoplastan interconnected liquid layer surrounding the cells. "We've found that plants that are able to move greater quantities of vitamin C into the leaf apoplast have a better chance of detoxifying ozone," says Burkey.
He has evidence that ozone tolerance in snap beans is associated with elevated vitamin C in the leaf apoplast. He has also found that plants vary widely in terms of how much vitamin C they make inside their cells. "But that doesn't seem to be related to how tolerant they are," says Burkey. While some plants make lots of vitamin C in their cells, they are not capable of transporting it into the apoplast, where it could provide protection against ozone injury.
After vitamin C neutralizes ROIs, the vitamin C itself becomes oxidized into dehydroascorbic acid (DHA). The plant then moves the DHA back into the cell where it is reduced, or revitalized, into vitamin C, which is once again available for transport back into the apoplast to fight ozone.
Questions remain about the protective importance of vitamin C stored in the apoplast before ozone exposure versus vitamin C that is pumped into the apoplast in response to ozone stress. But Burkey's most recent tests on snap beans suggest that the presence of vitamin C in the apoplast before ozone enters the leaf is critical.
He will next look more closely at how vitamin C and DHA are transported between the cell and the apoplast. And he will look for other antioxidant compounds in the leaf apoplast that could protect against ozone injury.
Burkey hopes the research will lead to finding genes associated with a plant's ability to pump vitamin C into the leaf apoplast. "You could potentially develop plants with greater ozone tolerance," he says. "Once you have the gene, you could express it in other plants using molecular techniques."By Rosalie Marion Bliss, Agricultural Research Service Information Staff."
