Parameters on Physiological Responses of Soybean (Glycine max Merr.) to Salinity

The mechanism imparting salt tolerance to crop plants remains still unsolved, although soybean has been classified as a susceptible plant to NaCl. To determine optimum parameters on physiological responses for improving sensitivity of salinity in breeding program, soybean (Glycine max Merr., cv. "Gwan-gan") plants were grown in a greenhouse, treated 20 days after emergence for 7 days with NaCl at 0, 30, 60, and 90mM, corresponding to electric conductivity of 1.2, 4.4, 7.3, and 10.4 dS/m, respectively, and assessed 30 days after treatment. Chlorophyll contents were significantly decreased by NaCl ($0.4{\sim}1.0\;mg/g$) compared to control (1.2 mg/g). Photosynthesis rate by NaCl treatment at $0{\sim}90\;mM$ at flowering stage was ranged from 5.0 (control) to $9.6\;{\mu}mol/m^2/s$. Oxygen for respiration was consumed from 5.4 to $9.7\;{\mu}mol/m^2/s$ so that the ratio of $O_2$ (evolution:consumption) was increased with the increase of NaCl, indicating that $O_2$ consumption seems to go beyond $O_2$ evolution. Water potential of leaf at vegetative stage II was ranged from -0.6 to -1.8 MPa and the highest level was observed at mid-day. Water potential by salt stress was decreased with range of $-2.1{\sim}-2.7MPa$ compared to control. Transpiration was decreased from 17% to 20% by NaCl stress. Water vapor diffusing resistance of intercellular air space was affected significantly, increasing up to $16{\sim}24%$ compared to control by NaCl treatment. Salt-treated soybean tended to accumulate $Na^+$, specially in root, with reduced absorption of N, P, $K^+$, $Ca^{2+}$, and $Mg^{2+}$ contents. Free proline content of soybean leaf as affected by different NaCl concentrations was increased 4.2 times ($184{\sim}434\;{\mu}g/g$) more than control. NaCl also increased activities of nitrate reductase and peroxidase by $28{\sim}161%$ and $3{\sim}22%$, respectively. The results show that physiological characteristics of soybean plants during assay were useful as the best parameters of salt stress or salt tolerance test to improve sensitivity in screening and breeding program among cultivars or germplasms.

염분에 대한 콩의 생리학적 반응지표 연구

본 연구는 "광안콩"의 20일 묘를 공시하여 $0{\sim}90\;mM$의 염분조건에서 콩의 생리학적 피해정도를 산정하고 내염성 품종선발과 육종계획에 요구되는 기초자료로 활용하고자 수행되었다. 엽록소의 함량은 정상적인 관수를 실시한 대조구에 비해 염분 처리에서 $15{\sim}60%$ 감소하였고 농도증가에 따라 감소정도가 크게 나타났다. 염분 처리에 따른 광합성과 호흡량은 각각 $28{\sim}48%$와 $16{\sim}34%$ 감소하였고 $O_2$ 생산 비율보다 $O_2$ 소모 비율이 높게 나타났다. 수분 potential은 정상 잎(-1.5 MPa)에 비해 염분처리에서는 농도별로 -2.13에서 -2.69 MPa로 직선적으로 감소하였다. 개화기 염처리에서 대조구 $13.3\;{\mu}g$의 약 $17{\sim}22%$로 감소한 $11.8{\sim}10.4\;{\mu}g$이었으며 증산저항은 $1.08{\sim}1.70\;S/m$로 증가하는 경향이었다. 콩 잎의 수분증산 저항에 미치는 염분의 영향은 잎 내부의 기층저항이 가장 심한 차이를 보였고 무처리에서 45.9 S/m인 반면 염분처리에서는 $53.5{\sim}56.6\;S/m$로 농도증가에 따라 증가하였으며 기공저항과 잎 경계면의 저항은 큰 차이를 보이지 않았다. 대부분의 무기물 함량은 뿌리보다 앞에서 축적량이 더 많게 나타났으나 $Na^+$만이 뿌리에 더 많이 축적되었고 N, P, $K^+$, $Ca^{2+}$ 및 $Mg^{2+}$는 무처리에 비해 오히려 그 축적량이 감소하였다. 염분처리에 따른 콩 잎의 유리 proline은 무처리($10.5\;{\mu}g$) 대비 $1.8{\sim}4.2$배 ($184{\sim}434\;{\mu}g$)로 염 농도가 증가함에 따라 축적량이 증가하는 경향이었다. Nitrate reductase의 활성은 염 농도가 증가함에 따라 증가하였으나 농도가 90 mM 염분 처리에서의 증가폭은 다소 둔화되는 경향이었다. 한편 peroxidase 활성 역시 염분농도가 증가함에 다라 증가하는 것으로 나타났다.