Unit Fresh Weight Basis Research Articles

Leaf growth in early development is key to biomass heterosis in Arabidopsis.

Arabidopsis thaliana hybrids have similar properties to hybrid crops, with greater biomass relative to the parents. We asked whether the greater biomass was due to increased photosynthetic efficiency per unit leaf area or to overall increased leaf area and increased total photosynthate per plant. We found that photosynthetic parameters (electron transport rate, CO2 assimilation rate, chlorophyll content, and chloroplast number) were unchanged on a leaf unit area and unit fresh weight basis between parents and hybrids, indicating that heterosis is not a result of increased photosynthetic efficiency. To investigate the possibility of increased leaf area producing more photosynthate per plant, we studied C24×Landsberg erecta (Ler) hybrids in detail. These hybrids have earlier germination and leaf growth than the parents, leading to a larger leaf area at any point in development of the plant. The developing leaves of the hybrids are significantly larger than those of the parents, with consequent greater production of photosynthate and an increased contribution to heterosis. The set of leaves contributing to heterosis changes as the plant develops; the four most recently emerged leaves make the greatest contribution. As a leaf matures, its contribution to heterosis attenuates. While photosynthesis per unit leaf area is unchanged at any stage of development in the hybrid, leaf area is greater and the amount of photosynthate per plant is increased.

A Positive Response of UV-B (280–320 nm) Enhanced Solar Radiation on the Growth and Physiological Activities of Mint (Mentha arvensisL.)

The changes in plant morphology, foliar characteristics and physiological parameters were studied in Menthaarvensis, an aromatic herb grown under UV-B (ultraviolet-B (280-320nm)) enhanced solar radiation (simulated to 6–24% O3 (ozone) depletion). UV-B enhancement was found to induce positive photomorphogenetic changes by increasing the fresh and dry weights. The SEM (scanning electron microscope) analysis of abaxial and adaxial leaf surfaces showed more oil glands with high stomatal frequency under enhanced UV-B when compared with ambient control. On unit fresh weight basis, Chl (chlorophyll) a and b and total Chl were enhanced in addition to the non-photosynthetic pigments such as flavonoids and anthocyanins. Measurement of photosynthetic efficiency in terms of fluorescence induction kinetics confirms that an alteration or redistribution of photosystems had occurred in Mentha offering resistance against UV-B. On the whole, a positive response at the level of morphology and physiological parameters was observed in Mentha seedlings grown under UV-B enhanced solar radiation.

A simple method for large scale estimation of leaf chlorophyll content in Hevea brasiliensis using a chlorophyll meter

Measurement of chlorophyll content of leaves by the conventional laboratory method involves discriminate sampling. weighing. extraction and spectrophotometric measurements that become laborious and time consuming especially when large number of samples is processed at a time. Nowadays, hand-held chlorophyll content meters are widely used for rapid and non-destructive estimation of chlorophyll content. Chlorophyll content in Hevea leaves was estimated spectrophotometrically by conventional extraction method and CCI values (chlorophyll content index) were recorded using a chlorophyll content meter, CCM - 200 (Opti-Sciences, USA) and regression models were developed. Significant positive linear relations between CCI and actual leaf chlorophyll content estimated by conventional extraction method were obtained. Separate equations were derived for determining chlorophyll content on unit fresh weight basis and unit leaf area basis. The method provides a rapid, accurate and non-destructive estimation of chlorophyll content of large number of leaves making the measurements simple and easy compared to conventional spectrophotometric assay.

Phytoplasma [Stolbur-subgroup (Bois Noir-BN)] infection inhibits photosynthetic pigments, ribulose-1,5-bisphosphate carboxylase and photosynthetic activities in field grown grapevine (Vitis vinifera L. cv. Chardonnay) leaves

In this work we have studied the influence of phytoplasma-induced grapevine yellows (yellowing) on some features of the thylakoids from field grown grapevine (Vitis vinifera L. cv. Chardonnay) leaves. Changes in photosynthetic pigments, soluble proteins, ribulose-1,5-bisphosphate carboxylase, photosynthetic activities and thylakoid membrane proteins were investigated. The level of total chlorophyll and carotenoids, on a unit fresh weight basis, showed a progressive decrease in phytoplasma infected leaves. Similar results were also observed for total soluble proteins and ribulose-1,5-bisphosphate carboxylase activity. When various photosynthetic activities were followed in isolated thylakoids, phytoplasma infection caused marked inhibition of whole chain and photosystem (PS) II activity. Smaller inhibition of PSI activity was observed even in severely infected leaves. The artificial exogenous electron donors, DPC and NH2OH significantly restored the PSII activity in both mild and severely infected leaves. The same results were obtained when Fv/ Fm was evaluated by Chl fluorescence measurements. The marked loss of PS II activity in infected leaves was evidently due to the loss of 33, 28–25, 23, 17 and 10kDa polypeptides. This conclusion was confirmed by immunological studies showing that the content of the 33kDa protein of the water-splitting complex was diminished significantly in infected leaves. Phytoplasma infection induced a fast degradation of LHCP II which became visible as yellowish colour in leaves.

Exclusion of solar UV-B (280–315 nm) radiation on vegetative growth and photosynthetic activities in Vigna unguiculata L.

The impact of solar radiation with and without UV-B component was studied in a tropical legume Vigna unguiculata L. The average level of ambient UV-B was 10 kJ m −2 day −1. Exclusion of solar UV-B increased the seedling height, leaf area and fresh weight. On a unit fresh weight basis, a 50% increase in total chlorophyll and 47% decrease in flavonoids was noticed after 20 days of growth. Decrease in flavonoid content in UV-B filtered seedlings indicates the plant responsiveness to minimal UV-B radiation existing inside the filter cage. UV-B exclusion during the early phase of seedling growth also promoted photosynthetic activities, measured as O 2 evolution or fluorescence transients. Such an enhancement in activity was attributed to modification in thylakoid organization under UV-B exclusion.

Decline in photosynthetic electron transport activity and changes in thylakoid protein pattern in field grown iron deficient Peach ( Prunus persica L.)

In this work we have studied the influence of lime-induced iron deficiency on some features of the thylakoids from peach trees grown in calcareous soils. Changes in photosynthetic pigments, soluble proteins, photosynthetic activities and thylakoid polypeptides were investigated. The level of total chlorophyll (Chl) and soluble proteins, on a unit fresh weight basis, showed a progressive decrease upon increase in iron deficient condition. When various photosynthetic activities were followed in isolated thylakoids, iron deficiency caused inhibition of whole chain and PS II activity. Smaller inhibition of PS I activity was observed even in severely chlorotic leaves. The artificial exogenous electron donor, Mn 2+ failed to restore PS II activity in both mildly and severely chlorotic leaves, while DPC and NH 2OH significantly restored the PS II activity in severely chlorotic leaves. The same results were obtained when F v/ F m was evaluated by Chl fluorescence measurements. The marked loss of PS II activity in thylakoids isolated from severely chlorotic leaves was due to the loss of D1 protein, 33, 23, 17 kDa extrinsic polypeptides, 28-25 kDa LHCP II polypeptides and 10 kDa polypeptide.

Changes induced by ultraviolet-B (280–320 nm) radiation to vegetative growth and photosynthetic characteristics in field grown Vigna unguiculata L.

The effect of ultraviolet-B (280–320 nm) radiation on growth and photosynthetic characteristics were investigated in field grown Vigna unguiculata L. Plants were grown at ambient and ambient plus a 1.8 kJ/m 2 supplementation of UV-B radiation for 25 days. The supplemental UV-B fluence used in this experiment simulated a 16% depletion in stratospheric ozone at midday in the summer at 10N latitude. Exposure to UV-B radiation had increased the plant height, leaf area and leaf biomass. The level of total chlorophyll on a unit fresh weight basis showed marginally decreased in the UV-B treated seedlings. No significant difference was seen in the concentration of UV-B absorbing compounds and RuBP case activity in UV-B treated seedlings. However, when various photosynthetic activities were followed in isolated chloroplasts, UV-B enhanced radiation stimulated the whole chain, photosystem (PS) I and PS II activity during the first 5 days. Prolonged treatment under UV-B enhanced radiation caused inhibition of the whole chain and the PS II activity. The artificial electron donor, Mn 2+ failed to restore UV-B radiation induced loss of PS II activity, while DPC and NH 2OH partially restored the PS II activity.

Acid rain: Acidic mist-induced response in growth and photosynthetic activities on crop plants

Experiments were conducted in the field to investigate the influence of acidic mists treatment on height, biomass, leaf chlorophyll, net photosynthesis, and photosystem activities in Vigna sinensis L. and Phaseolus mungo L. Plants exposed to different acidic mists (pH 5, 4, 2) for 5 days showed significant reduction in height and biomass accumulation. The level of chlorophyll on a unit fresh weight basis showed progressive reduction upon increasing acidity of mists treatment; the reduction was due to the loss of Chl a and Chl b. Leaf-soluble protein was not significantly reduced. The increased stomatal diffusive resistance and reduced photosynthetic pigments lowered the net photosynthetic rate. However, when various photosynthetic activities were followed in isolated chloroplast, a decrease in the rates was obtained in the seedlings exposed to pH 4 and 2. No significant change in photosystem I activity was observed at various acidic mists treatments. Analysis of chloroplast polypeptides indicates specific loss of 33, 23, and 17 kDa extrinsic polypeptides.

Photosynthetic and leaf morphological characteristics in Leucaena leucocephala as affected by growth under different neutral shade levels

Morphological and physiological measurements on individual leaves of Leucaena leucocephala seedlings were used to study acclimation to neutral shading. The light-saturated photosynthetic rate (Pn max) ranged from 19.6 to 6.5 μmol CO2 m(-2) s(-1) as photosynthetic photon flux density (PPFD) during growth decreased from 27 to 1.6 mol m(-2) s(-1). Stomatal density varied from 144 mm(-2) in plants grown in high PPFD to 84 mm(-2) in plants grown in low PPFD. Average maximal stomatal conductance for H2O was 1.1 in plants grown in high PPFD and 0.3 for plants grown in low PPFD. Plants grown in low PPFD had a greater total chlorophyll content than plants grown in high PPFD (7.2 vs 2.9 mg g(-1) on a unit fresh weight basis, and 4.3 vs 3.7 mg dm(-2) on a unit leaf area basis). Leaf area was largest when plants were grown under the intermediate PPFDs. Leaf density thickness was largest when plants were grown under the largest PPFDs. It is concluded that L. leucocephala shows extensive ability to acclimate to neutral shade, and could be considered a facultative shade plant.

The effect of nutrient deficiencies on phosynthesis and respiration in spinach

Spinach plants were grown in nutrient-culture solutions containing reduced levels of all the macro- and micro-nutrient elements except cobalt and chlorine. The rates of photosynthesis (carbon dioxide fixation in the light expressed on a per unit chlorophyll or per unit fresh-weight basis) and respiration (carbon dioxide evolution in the dark expressed on a per unit nitrogen or per unit fresh-weight basis) for whole plants were measured using infra-red gas analysis techniques. Measurements were made when the plants displayed clear symptoms of deficiency relative to control plants. All nutrient deficiencies except iron and molybdenum depressed photosynthesis when chlorophyll was the basis of calculation; manganese-, copper-, phosphorus- and potassium-deficient plants showed the greatest depression. Alternatively when photosynthesis was calculated on a fresh weight basis calcium was the only deficiency which had no affect. Similarly when respiration was calculated on a nitrogen basis all deficiencies except iron, molybdenum and nitrogen result in depressed rates but when respiration was expressed on a fresh-weight basis potassium deficiency resulted in enhanced respiration rates and nitrogen, phosphorus, sulphur, manganese, zinc and molybdenum deficiencies resulted in reduced respiration rates.