Fumitake Kubota

Correlation of Chlorophyll Meter Readings with Gas exchange and Chlorophyll Fluorescence in Flag Leaves of Rice (Oryza sativa L.) Plants

Abstract The objective of this study was to establish the correlation of the chlorophyll meter (SPAD) readings with the contents of chlorophyll (Chl) and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), the gross photosynthetic rate (Pg), and the maximum quantum yield of photosystem II (PSII) (Fv/Fm) in flag leaves of rice (Oryza sativa L.) in ripening stage. The SPAD readings significantly correlated with the Chl content, the Rubisco content, Pg and Fv/Fm (R2 = 0.848, 0.648, 0.671 and 0.712, respectively), which suggests that the SPAD meter has the potential to estimate the photosynthetic capacity of the flag leaves. However, both Pg and Fv/Fm had a stronger relationship with the Rubisco content than the SPAD readings, indicating that the PSII photochemical and CO2 assimilation capacities are strongly influenced by the Rubisco content. Therefore, accurate calibration would be indispensable to obtain the physiological information from the SPAD readings of flag leaves.

Characteristics of Gas Exchange and Chlorophyll Fluorescence during Senescence of Flag Leaf in Different Rice (Oryza sativa L.) Cultivars Grown under Nitrogen-Deficient Condition

Abstract Effects of nitrogen (N) deficiency on photosynthetic gas exchange and photosystem II (PSII) photochemistry of flag leaves during grain-filling stage were investigated in six rice cultivars, Kasalath (a conventional indica), IR36 (an improved indica), Shirobeniya (a conventional japonica), Nipponbare (an improved japonica), Akenohoshi (an improved japonica-indica intermediate type) and BSI429 (an improved tropical japonica, a new plant type line) grown hydroponically in N-sufficient (NS) and N-deficient (ND) solution. From 3 to 24 days after heading (DAH), net photosynthetic rate (Pn), maximum quantum yield of photosystem II (PSII) (Fv/Fm), quantum yield of PSII electron transport ( Φpsii), and contents of chlorophyll (Chl) and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) in the flag leaves decreased, particularly under the ND condition in all six cultivars. A substantial difference was observed among the ND plants for the sustainability index (SI, the ratio of the value at 24 DAH to that at 3 DAH) of Pn, Fv/Fm, Φpsii, Chl content and Rubisco content; SIs of those parameters of Akenohoshi, BSI429, Nipponbare and Shirobeniya were higher than those of IR36 and Kasalath. The SI of Pn showed significant positive correlations with those of Fv/Fm, Φpsii, and the contents of Chl and Rubisco under the ND condition. It was concluded that the sustainability of photosynthesis in the flag leaves was mainly due to those of PSII photochemistry and electron transport, which was associated with the maintenance of Chl and Rubisco under the ND condition.

Effects of nitrogen supply restriction on gas exchange and photosystem 2 function in flag leaves of a traditional low-yield cultivar and a recently improved high-yield cultivar of rice (Oryza sativa L.)

The effects of nitrogen (N) supply restriction on the CO2 assimilation and photosystem 2 (PS2) function of flag leaves were compared between two contrastive Japanese rice cultivars, a low-yield cultivar released one century ago, cv. Shirobeniya (SRB), and a recently improved high-yield cultivar, cv. Akenohoshi (AKN). Both cultivars were solution-cultured at four N supply levels from N4 (control) to N1 (the lowest). With a reduction in N-supply, contents of N (LNC), ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO), and chlorophyll (Chl) in flag leaves decreased in both cultivars. In parallel with this, the net photosynthetic rate (PN), mesophyll conductance (gm), and stomatal conductance (gs) decreased. PN was more dominantly restricted by gm than gs. The values of PN, gm, and RuBPCO content were larger in AKN than SRB at the four N supply levels. The content of Chl greatly decreased with N deficiency, but the reduction in the maximum quantum yield of PS2 was relatively small. Quantum yield of PS2 (ΦPS2) decreased with N deficiency, and its significant cultivar difference was observed between the two cultivars at N1: a high value was found in AKN. The content ratio of Chl/RuBPCO was also significantly low in AKN. The low Chl/RuBPCO is one of the reasons why AKN maintained a comparatively high PN and ΦPS2 at N deficiency. The adequate ratio of N distribution between Chl and RuBPCO is the important prerequisite for the efficient and sustainable photosynthesis in a flag leaf of rice plant under low N-input.

The effects of drought stress and leaf ageing on leaf photosynthesis and electron transport in photosystem 2 in sweet potato (Ipomoea batatas Lam.) cultivars

Of the four tested sweet potato cultivars having different features in growth and yield, cv. Koganesengan (KOG) was sustainable in photosynthetic activity through young to aged leaves under drought. One of the causes for this phenomenon may be stomatal conductance (gs) of this cultivar that was relatively high in both aged and drought-imposed leaves. In these leaves the non-photochemical quenching (NPQ) was low and the quantum yield of photosystem 2 (Φe) was high, compared to those of the other cultivars. This helps to prevent excessive accumulation of chemical energy in leaves and a decrease in photoinhibition damage to the photosynthetic function, by which KOG sustains a relatively high photosynthetic activity under the drought and alleviates functional deterioration caused by leaf age.

The relationship between canopy structure and high productivity in napier grass, Pennisetum purpureum Schumach

Abstract The vigorous growth and high production potential of napier grass ( Pennisetum purpureum Schumach) have been reported at various sites in the tropics and also in the temperature zone, including Japan. A large structural change of the canopy with growth is a prominent feature of this species. This study investigated the high productivity of napier grass in relation to structural features of the canopy. Young shoots (cv. Merkeron) were transplanted in a field and grown for 102 days. The final dry matter of aboveground parts was 2.7 kg m −2 and the maximum crop growth rate (CGR) was 58.0 g m −2 d −1 . As leaf area index (LAI) increased from 0.7 to 15.4 with growth, light extinction coefficient ( K ) of the canopy decreased gradually from 1.1 to 0.38 due to elongation and erection of stems. K varied primarily as a function of stem inclination and length. The structural change of the canopy from planophile to erectophile with growth protects lower leaves from heavy shading, allowing the canopy to approximate an optimum LAI throughout the growth period. This is regarded as the main cause of high productivity of this species.

Estimation of Photosynthetic Activity from the Electron Transport Rate of Photosystem 2 in a Film-Sealed Leaf of Sweet Potato, Ipomoea batatas Lam

In order to evaluate the photosynthetic activity of a C3 leaf from the electron transport rate (ETR) of photosystem 2 (PS2), a new method was devised and examined using leaves of sweet potato. In this method, both surfaces of a leaf were sealed with transparent films to stop the gas exchange between the leaf and the atmosphere; hence the functions of both photosynthetic assimilation (CO2 uptake) and photorespiration (CO2 release) are restricted to the inside of the leaf. After both functional rates became equally balanced, ETR of the sealed leaf (ETRseal) was determined from the chlorophyll fluorescence. The measurements were conducted at different irradiances and leaf temperatures and by using leaves of different age. Under each measurement condition, ETRseal showed a close positive relationship with the photosynthetic potential, or the gross photosynthetic rate measured in the air of 2 % O2 (PG2%) before sealing. ETRseal may become an indicator to estimate or evaluate the photosynthetic activity of C3 leaves.

Estimation of Photorespiration Rate by Simultaneous Measurements of CO2, Gas Exchange Rate, and Chlorophyll Fluorescence Quenching in the C3 Plant Vigna Radiata (L.) Wilczek and the C4 Plant Amaranthus Mongostanus L.

So far the photorespiration rate (RP) in a leaf has been determined as the difference between the net photosynthetic rates (PN) measured in 21 % O2 air (PN21%) and 3 % O2 air (PN3%). In the C3 plant Vigna radiata and the C4 plant Amaranthus mongostanus L., PN and chlorophyll fluorescence quenching in leaves were monitored simultaneously. RP of leaves in situ was estimated as termed RPE from the electron transport rates through photosystem 2 (PS2), and compared with RPO (PN3% − PN21%). In V. radiataRPO was 11.9 µmol(CO2) m−2 s−1 and the ratio of RPO to PN21% was 42.2 %, whereas the ratio of RPE to PN21% was 25.7 %. This suggests that RPO may be over-estimated for the real RP in normal air. In A. mongostanus, PN was almost not changed with a decrease in O2 concentration from 21 to 3 %, whereas the quantum yield of PS2 was evidently affected by the change in O2 concentration. This fact shows the presence of photorespiration in this C4 species, where RPE was equivalent to 3.8 % of PN21%.

Effects of Shading on Hydraulic Resistance and Morphological Traits of Internode and Node of Napiergrass (Pennisetum purpureum Schumach.)

Received 9 February 2007. Accepted 9 January 2008. Corresponding author: K. Nagasuga (nkiyoshi@bio.mie-u.ac.jp, fax +81-059-230-1463, present address; Kii Kuroshio Bio-regional Field Science Center, Faculty of Bioresources, Mie University, Takanoo, Tsu 514-2221, Japan). Effects of Shading on Hydraulic Resistance and Morphological Traits of Internode and Node of Napiergrass (Pennisetum purpureum Schumach.)

Characteristics of nutrient absorption and water purification in some plant species grown by floating culture system

Abstract Nutrient absorption and water purification by rice (Oryza sativa L.), canna (Canna indica L.), reed (Phragmites communis Trin.), and umbrella plant (Cyperus alternifolius L.), grown by the floating culture system, were compared under different pH conditions in natural water. The pH of the rooting zone in natural water changed due to the increase in the CO2 concentration associated with root respiration, which was achieved by placing the roots in a plastic pot attached beneath the float to isolate the roots from the outside water. The absorption of nutrients (N and P) by umbrella plants was higher than that by the other plant species and was not inhibited by high pH values. In addition, the absorption of nutrients (N, P, K, and Fe) by umbrella plants increased with the application of a slow-release fertilizer to the basal part of the roots. As a result, umbrella plants grown with fertilizer displayed a strong water purification effect, regardless of the pH values. On the other hand, nutrient absorption by rice was severely inhibited by high pH values when fertilizer was applied. This was because the absorption of Nand P increased with fertilizer application, while the absorption of Fe by rice was markedly reduced under high pH conditions, resulting in iron deficiency. Therefore, we suggest that species tolerant to high pH conditions, such as umbrella plants, should be selected and that fertilizer should be applied to those plants, although the levels of the nutrients contained in the fertilizer should not exceed those corresponding to the absorption capacity of the plant, for improving water quality in closed natural water bodies with high pH values

Concurrent Monitoring of Oxygen Evolution and Chlorophyll Fluorescence in Mungbean Leaves with a Liquid-Phase Oxygen Electrode

In the liquid-phase oxygen electrode, photosynthetic rate is determined by the rate of oxygen evolution from sliced leaf pieces stirred in CO2-saturated reaction solution. The slicing and stirring treatments promote CO2 absorption of leaf pieces, but there is some difficulty in determining fluorescence emittance from the moving objectives. The barrier of CO2 uptake into leaf was removed by peeling its epidermis, and oxygen evolution rates from peeled leaves were readily measured (Yatomi, M. et al. 1992). A liquid-phase oxygen electrode was partly improved to make concurrent measurements of oxygen evolution rate and chlorophyll fluorescence quenching. In this study, we used this tool and observe the responses of gross oxygen evolution rate (Og), the quantum yield of PSII ( e) and photorespiration rate (Pr) to the changes of photosynthetic environment.