Sains Malaysiana 46(2)(2017): 189–195

http://dx.doi.org/10.17576/jsm-2017-4602-02

Nitric Oxide Increases Pb Tolerance by Lowering Pb Uptake and Translocation as well as Phytohormonal Changes in Cowpea (Vigna unguiculata (L.) Walp.)

(Nitrik Oksida Meningkatkan Toleransi Pb dengan Menurunkan pengambilan Pb dan Translokasi serta Perubahan Fitohormon dalam Kacang Panjang (Vigna unguiculata (L.) Walp.))

OMID SADEGHIPOUR*

Department of Agronomy, Yadegar-e-Imam Khomeini (RAH) Shahre-rey Branch, Islamic Azad University, Tehran, Iran

Received: 11 August 2015/Accepted: 16 May 2016

ABSTRACT

Lead (Pb) is one of the most abundant toxic heavy metals which adversely affected growth and yield of crop plants. Nitric oxide (NO), an endogenous signaling molecule, has been suggested to be involved in defense responses to biotic and abiotic stresses in plants. The present study was done to induce Pb tolerance in cowpea plants by exogenous NO application using two levels of Pb, 0 and 200 mg Pb (NO₃)₂ kg^-1 soil and three NO levels, 0, 0.5 and 1 mM sodium nitroprusside (SNP), as NO donor. The results showed that Pb treatment caused a significant increase in Pb concentration in all plant parts. Roots had higher levels of Pb than the stems, leaves and seeds. Furthermore, lead toxicity reduced auxin (IAA), cytokinin and gibberellic acid (GA₃) content but increased abscisic acid (ABA) level. Moreover Pb stress decreased stomatal conductance, leaf area and consequently seed yield of cowpea. Exogenous application of NO at 0.5 mM noticeably alleviated the lead toxicity by improving the leaf area, stomatal conductance and seed yield. NO increased Pb tolerance by lowering Pb uptake and translocation, enhancing the promoting phytohormone (IAA, cytokinin and GA₃) level and reducing ABA content.

Keywords: Leaf area; Pb toxicity; plant hormones; seed yield; stomatal conductance

ABSTRAK

Plumbum (Pb) merupakan salah satu logam berat toksik paling banyak yang telah menjejaskan pertumbuhan dan hasil tanaman tumbuhan. Nitrik oksida (NO), molekul isyarat endogen disyaki terlibat dalam tindakan pertahanan terhadap stres biotik dan abiotik dalam tumbuh-tumbuhan. Kajian ini dijalankan untuk mengaruh toleransi Pb dalam tumbuhan kacang panjang dengan aplikasi NO eksogen menggunakan dua tahap Pb, 0 dan 200 mg Pb (NO₃)₂ kg^-1 tanih dan tiga peringkat NO, 0, 0.5 dan 1 mM sodium nitroprusid (SNP), sebagai penderma NO. Keputusan kajian menunjukkan bahawa rawatan Pb telah menyebabkan peningkatan ketara dalam kepekatan Pb pada semua bahagian tumbuhan. Akar mempunyai tahap Pb yang lebih tinggi daripada batang, daun dan biji benih. Selain itu, ketoksikan plumbum mengurangkan kandungan auksin (IAA), sitokinin dan asid giberelik (GA₃) tetapi meningkatkan tahap asid absisik (ABA). Tambahan pula tekanan Pb mengurangkan konduktans stoma, keluasan daun dan penghasilan biji benih kacang panjang. Aplikasi eksogen NO pada 0.5 mM didapati mengurangkan keracunan plumbum dengan memperbaiki keluasan daun, konduktans stoma dan hasil biji benih. NO meningkatkan toleransi Pb dengan mengurangkan penyerapan Pb dan translokasi, menggalakkan peningkatan tahap fitohormon (IAA, sitokinin dan GA₃) serta mengurangkan kandungan ABA.

Kata kunci: Hasil benih; hormon tumbuhan; keluasan daun; ketoksikan PB; konduktans stoma

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*Corresponding author; email: osadeghipour@yahoo.com