121 Ann. appl. Biol. (2003), 143:121-124 Printed in UK *Corresponding Author E-mail: shayat@lycos.com ' 2003 Association of Applied Biologists Soaking seeds of Lens culinaris with 28-homobrassinolide increased nitrate reductase activity and grain yield in the field in India By S HAYAT* and A AHMAD Plant Physiology Section, Department of Botany, Aligarh Muslim University, Aligarh-202002, India (Accepted 17 February 2003; Received 4 October 2002) Summary Surface-sterilised seeds of Lens culinaris cv. Pusa-6 were soaked in 0 M, 10 -6 M, 10 -8 M or 10 -10 M aqueous solutions of 28-homobrassinolide (HBR) for 4 h, 8 h or 12 h and planted in the field in a sandy loam soil. Plants were sampled 60, 90 and 120 days after sowing (DAS). Soaking with HBR decreased root length and nodule number per plant but increased nitrate reductase activity (E.C.1.6.6.1). Soaking with HBR also increased grain yield at the final harvest 140 DAS. The greatest increase was obtained with an HBR concentration of 10 -8 M. Key words: Brassinosteroids, root length, root nodule number, nitrate reductase activity Introduction Brassinosteroids (BS) are natural plant growth regulating substances with structural similarities to animal steroidal hormones. They have a wide distribution in the plant kingdom and have been demonstrated to play a role in stem elongation, pollen tube growth, leaf bending and epinasty, root growth inhibition, induction of ethylene biosynthesis, proton pump activation, xylem differentiation and regulation of gene expression (Khripach et al., 2000). Exogenous application of BS to plants can have a growth-promotive effect (Sakurai and Fujioka, 1993) and can increase carbonic anhydrase and nitrate reductase activities (Hayat et al ., 2001 a,b ). Brassinosteroids have been employed for economic gain, as the treated plants develop greater resistance to stress and produce more seeds in many crop plants (Cutler et al., 1991; Hayat et al., 2000, 2001b). In contrast, rooting and subsequent growth was inhibited by 24-epibrassinolide (Roddick & Guan, 1991) and brassinolide (Jones-Held et al., 1996). In this paper we investigate relationships between the nodule bearing capacity and some related aspects of nitrogen metabolism with 28-homobrassinolide (HBR) in the field. The approach used was to grow a crop of Lens culinaris L. Medic from seeds soaked in an aqueous solution of the steroid. In this study, HBR was used because it is more active and stable in field trials than some other brassinosteroids (Khripach et al., 2000). Materials and Methods Seeds Seeds of Lens culinaris cv. Pusa-6 were purchased from National Seed Corporation Ltd., New Delhi, India. Field experimentation The experiment was conducted during the winter season of 1999-2000 at the Rafi Ahmad Kidwai Institute of Agricultural Sciences, Aligarh Muslim University, Aligarh, India. The soil was a sandy loam of pH 7.8 and contained; available N, 235 kg ha -1 ; available P, 18.3 kg ha -1 and available K, 660 kg ha -1 . A recommended basal dose of 45 kg N as urea, 45 kg P as monocalcium superphosphate and 30 kg K ha -1 as muriate of potash was applied to each plot before sowing. Surface-sterilised (0.1 % mercuric chloride solution) healthy seeds were soaked in water (control), 10 -6 M, 10 -8 M or 10 -10 M aqueous solution of 28-homobrassinolide for 4 h, 8 h or 12 h, giving a 4 × 3 factorial structure. Soaked seeds were uniformly inoculated with Rhizobium sp. and sown on 2 November 1999. The experiment was laid out in five replicate randomised complete blocks, giving a total of 60 plots of 5 m 2 . Seeds were dibbled in rows 60 cm apart and with an in-row spacing of 40 cm at the rate of 50 kg ha -1 . Sampling Plants were sampled at 60, 90 and 120 days after sowing (DAS). At each sampling, five plants per plot from each treatment were dug out with the soil and transferred to a bucket filled with water to remove the soil adhering to the roots. Root length was measured and nodule number counted. At maturity of the crop, 140 DAS, the remaining plants were cut at the base and pods per plant, pod length, seed number per pod, 1000 seed weight and seed yield per plot were determined.