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Photosynthetic characteristics and carbon partitioning in the virus-eradicated and virus-infected Oncidium Gower Ramsey under different growth irradiances
Author
Ouyang, Wen
Supervisor
He, Jie
Chia, Tat Fatt
Abstract
Effects of different growth irradiances on photosynthetic capacities were examined in the virus-eradicated and virus-infected Oncidiunz Gower Ramsey grown under natural and controlled conditions. Under natural condition, plants were grown under 30% of prevailing solar radiation and transferred from 30% to 60% and to 100% of prevailing solar radiation. Both virus-infected and virus-eradicated plants that were transferred from 30% to 60% of prevailing solar radiation for two weeks exhibited the highest photosynthetic 02 evolution, maximum A and gs, followed by those plants maintained at 30% of prevailing solar radiation. The plants transferred from 30% to 100% of prevailing solar radiation for two weeks exhibited the lowest values of these parameters. All these parameters of the virus-eradicated plants were significant higher than those of the virus-infected plants after the plants transferred from 30% to 60% of prevailing solar radiation for two weeks. However, the differences in these parameters between the virus-infected and virus-eradicated plants measured at 30% and those transferred from 30% to 100% of prevailing solar radiations were not significant.
Midday Fv/Fm, ratio depression indicated that dynamic photoinhibition occurred in both virus-infected and virus-eradicated Oncidium Gower Ramsey grown under all three light conditions. However, chronic photoinhibition occurred only in those transferred from 30% to 100% of prevailing solar radiation. Moreover, the virus infected Oncidium Gower Ramsey was more susceptible to high irradiance than the virus-eradicated plants. Over the 2-week treatment period, sustained decreases in predawn Fv/Fm, were observed in both virus-nfected and virus-eradicated plants transferred from 30% to 100% of prevailing solar radiation. The light regimes used to determined qP and qN at laboratory were according to maximum PFDs under which the plants were grown. There were no significant differences of qP and qN between the virus-infected and virus-eradicated plants under 30% of prevailing solar radiation, qP decreased slower and qN increased faster in the virus-eradiated plants than those of the virus-infected plants exposed to higher PFDs in the plants transferred from 30% to 60% of prevailing solar radiation. However, for the plants transferred from 30% to 100% of prevailing solar radiation, qP of the virus-infected plants showed faster decrease than those of the virus-eradicated plants, but there were no significantly different in qN between the virus-infected and virus-eradicated plants exposed to all PARS.
There were significant differences in total chlorophyll content and chlorophyll/carotenoid between the virus-infected and virus-eradicated plants grown under 30% and those transferred from 30% to 60% of prevailing solar radiations. Whereas total chlorophyll content and chlorophyll/carotenoid ratio significantly reduced for the plants transferred from 30% to 100% of prevailing solar radiation. In contrast, the chlorophyll a/b ratio increased with the increase of irradiance. There were no significant differences in caroteniod between the virus-eradicated and virus-infected plants under all three irradiances. Over the 2-week treatment period, lowered chlorophyll contents were observed in both virus-infected and virus-eradicated plants transferred from 30% to 100% of prevailing solar radiation. Total leaf nitrogen contents, soluble and Rubisco protein contents and Rubisco activity remained stable during 35 days of measurements for the plants grown under 30% of prevailing solar radiation. For those plants transferred from 30% to 60% of prevailing solar radiation for 35 days, however, theses three parameter significantly increased. When plants transferred from 30% to 100% of prevailing solar radiation, these parameters were lower compared to their control plants maintained at 30% of prevailing solar radiation after 35 days of light transfer. Total leaf nitrogen contents, soluble and Rubisco protein contents and Rubisco activity were significant higher in the virus-eradicated plants compared to those of the virus-infected plants under whole treatments (excluding the total leaf nitrogen contents and Rubisco activities of the plants grown at 30% of prevailing solar radiation).
The plants transferred from 30% to 60% of prevailing solar radiation for 48 days had highest leaf area, fresh and day weights of leaves and water content. However, the plants transferred from 30% to 100% of prevailing solar radiation had lowest values of the growth parameters. Moreover, the virus-eradicated plants had much higher values of leaf area, fresh and dry weights and water content compared to that of virus-infected plants. The virus-eradicated plants also had faster leaf emergence rate, longer inflorescence, much more inflorescence branches and flowers; greater basal in florescence stalk diameter and larger flower petal average area as well as greater fresh and dry weights of pseudobulb and water content of pseudobulb than the virus-infected plants.
I4c feeding experiment was performed with plants transferred from 30% to 60% of prevailing solar radiation for 1 year. The virus-eradicated plants had significant high I4c assimilate exports compared to the virus-infected plants after feeding I4c for 29 h. Leaves and pseudobulbs were the main sinks after I4c feeding of plants for 5 h. Between 29 to 77 h after I4c feeding, inflorescence captured most of 14c compared to other parts of plants. The virus-eradicated plants obtained more than the virus-infected plants during this period. However, when C feeding extended to 54 h, the roots of the virus-infected plants captured 2-fold than the virus-eradicated plants.
In order to further investigate the effects of light and temperature on the plants, both detached leaves and whole plants were exposed to different PFDs at 28°C and 35°C. Exposed to PFDs of 300 and 600 μmol m-2 s-1 at 28°C, Fv/Fm and chlorophyll content of the detached leaves kept stable from 5 to 25 h. However, Fv/Fm, and chlorophyll content decreased when PFDs increased up to 1200 and 1500 μm01 m-2 S-1. At 35°C, Fv/Fm and chlorophyll content showed decreases at all PFDs from 5 to 25 h. When the whole plants exposed to a PFD of 300 μm01 m-2 S-1 at 28'C and 35°C for 3 days, neither the virus-infected nor virus-eradicated plants showed change in Fv/Fm and chlorophyll content compared to those plants grown under 60% of prevailing solar radiation under the natural conditions used as control. When the light intensity increased to a PFD of 1200 μm01 m-2 s-1 at 28°C and 35°C, all plants exhibited decreases in both FJF, ratios and chlorophyll contents compared to their control.
Susceptibility of the virus-infected and virus-eradicated plants to different lights and temperatures and the relations among the parameters studied were discussed.
Midday Fv/Fm, ratio depression indicated that dynamic photoinhibition occurred in both virus-infected and virus-eradicated Oncidium Gower Ramsey grown under all three light conditions. However, chronic photoinhibition occurred only in those transferred from 30% to 100% of prevailing solar radiation. Moreover, the virus infected Oncidium Gower Ramsey was more susceptible to high irradiance than the virus-eradicated plants. Over the 2-week treatment period, sustained decreases in predawn Fv/Fm, were observed in both virus-nfected and virus-eradicated plants transferred from 30% to 100% of prevailing solar radiation. The light regimes used to determined qP and qN at laboratory were according to maximum PFDs under which the plants were grown. There were no significant differences of qP and qN between the virus-infected and virus-eradicated plants under 30% of prevailing solar radiation, qP decreased slower and qN increased faster in the virus-eradiated plants than those of the virus-infected plants exposed to higher PFDs in the plants transferred from 30% to 60% of prevailing solar radiation. However, for the plants transferred from 30% to 100% of prevailing solar radiation, qP of the virus-infected plants showed faster decrease than those of the virus-eradicated plants, but there were no significantly different in qN between the virus-infected and virus-eradicated plants exposed to all PARS.
There were significant differences in total chlorophyll content and chlorophyll/carotenoid between the virus-infected and virus-eradicated plants grown under 30% and those transferred from 30% to 60% of prevailing solar radiations. Whereas total chlorophyll content and chlorophyll/carotenoid ratio significantly reduced for the plants transferred from 30% to 100% of prevailing solar radiation. In contrast, the chlorophyll a/b ratio increased with the increase of irradiance. There were no significant differences in caroteniod between the virus-eradicated and virus-infected plants under all three irradiances. Over the 2-week treatment period, lowered chlorophyll contents were observed in both virus-infected and virus-eradicated plants transferred from 30% to 100% of prevailing solar radiation. Total leaf nitrogen contents, soluble and Rubisco protein contents and Rubisco activity remained stable during 35 days of measurements for the plants grown under 30% of prevailing solar radiation. For those plants transferred from 30% to 60% of prevailing solar radiation for 35 days, however, theses three parameter significantly increased. When plants transferred from 30% to 100% of prevailing solar radiation, these parameters were lower compared to their control plants maintained at 30% of prevailing solar radiation after 35 days of light transfer. Total leaf nitrogen contents, soluble and Rubisco protein contents and Rubisco activity were significant higher in the virus-eradicated plants compared to those of the virus-infected plants under whole treatments (excluding the total leaf nitrogen contents and Rubisco activities of the plants grown at 30% of prevailing solar radiation).
The plants transferred from 30% to 60% of prevailing solar radiation for 48 days had highest leaf area, fresh and day weights of leaves and water content. However, the plants transferred from 30% to 100% of prevailing solar radiation had lowest values of the growth parameters. Moreover, the virus-eradicated plants had much higher values of leaf area, fresh and dry weights and water content compared to that of virus-infected plants. The virus-eradicated plants also had faster leaf emergence rate, longer inflorescence, much more inflorescence branches and flowers; greater basal in florescence stalk diameter and larger flower petal average area as well as greater fresh and dry weights of pseudobulb and water content of pseudobulb than the virus-infected plants.
I4c feeding experiment was performed with plants transferred from 30% to 60% of prevailing solar radiation for 1 year. The virus-eradicated plants had significant high I4c assimilate exports compared to the virus-infected plants after feeding I4c for 29 h. Leaves and pseudobulbs were the main sinks after I4c feeding of plants for 5 h. Between 29 to 77 h after I4c feeding, inflorescence captured most of 14c compared to other parts of plants. The virus-eradicated plants obtained more than the virus-infected plants during this period. However, when C feeding extended to 54 h, the roots of the virus-infected plants captured 2-fold than the virus-eradicated plants.
In order to further investigate the effects of light and temperature on the plants, both detached leaves and whole plants were exposed to different PFDs at 28°C and 35°C. Exposed to PFDs of 300 and 600 μmol m-2 s-1 at 28°C, Fv/Fm and chlorophyll content of the detached leaves kept stable from 5 to 25 h. However, Fv/Fm, and chlorophyll content decreased when PFDs increased up to 1200 and 1500 μm01 m-2 S-1. At 35°C, Fv/Fm and chlorophyll content showed decreases at all PFDs from 5 to 25 h. When the whole plants exposed to a PFD of 300 μm01 m-2 S-1 at 28'C and 35°C for 3 days, neither the virus-infected nor virus-eradicated plants showed change in Fv/Fm and chlorophyll content compared to those plants grown under 60% of prevailing solar radiation under the natural conditions used as control. When the light intensity increased to a PFD of 1200 μm01 m-2 s-1 at 28°C and 35°C, all plants exhibited decreases in both FJF, ratios and chlorophyll contents compared to their control.
Susceptibility of the virus-infected and virus-eradicated plants to different lights and temperatures and the relations among the parameters studied were discussed.
Date Issued
2000
Call Number
QK495.O64 Ouy
Date Submitted
2000