Identification and evaluation of excess nitrate-responsive genes in celery (Apium graveolens L.) roots

Abstract

SummarySalinity negatively impacts plant growth and productivity, but little is known about nitrate stress responses in celery (Apium graveolens L.). To improve our understanding of the adaptation of celery in nitrate-rich environments, we constructed a suppression-subtractive hybridisation (SSH) library. cDNAs from celery root tissue exposed to 100 mM total nitrate for 2, 4, 8, 24, 48, or 72 h were used as testers, and cDNAs of roots exposed to 0 mM nitrate for the same treatment times were used as drivers. Sequence analysis of the SSH cDNA library generated 202 high-quality expression sequence tags (ESTs), of which 112 were non-redundant. Eighty ESTs showed similarities to proteins of known function, and could be categorised into 11 functional groups, including metabolism, protein synthesis, cell defense and rescue, signal transduction, transport facilitation, genetic information processing, energy, cell structure, transcription, unknown, and no hits. Ten of the ESTs were selected by reverse transcription (RT)-PCR and their induction by nitrate stress was confirmed. An analysis of the physiological changes in celery roots indicated that hydrogen peroxide (H2O2) and malondialdehyde (MDA) levels increased rapidly under the 100 mM total nitrate stress treatment. The expression of genes encoding peroxidase (POD), glutamine synthetase (GS), and a proline-rich protein (PRP) were up-regulated. The maximum activities of POD and GS, and free proline (Pro) contents were found 48 h and 72 h after 100 mM nitrate treatment. Collectively, these results contribute to our understanding of the molecular mechanism(s) of nitrate tolerance in celery, and possibly in other species.