Effects of Cd²⁺stress on radish (Raphanus sativus) seedling growth based on proteome technique

Three-day-old radish seedlings were treated with 10~150 mmol·L^-1 Cd²⁺ for 12 h for determination of the effects of Cd²⁺ on seedling growth and proteome by using 2-DE technique and MALDI-TOF MS. The results showed an obvious inhibition of seedling growth. Seedling height decreased from 3.80±0.68 cm under the control to 3.41±0.64 cm under 10 mmol·L^-1 Cd²⁺ treatment (P < 0.01), 1.61±0.37 cm under 50 mmol·L^-1Cd²⁺ treatment (P < 0.01), 1.26±0.11 cm under 100 mmol·L^-1 Cd²⁺ treatment (P < 0.01) and to 0.80±0.14 cm under 150 mmol·L^-1 Cd²⁺ treatment (P < 0.01). Root growth was also obviously inhibited. Cell mitotic inhibition was noted in root tip meristem. Seedling fresh weight decreased from 10.92±0.86 g under the control to 9.93±0.77 g under 10 mmol·L^-1, 4.52±0.13 g under 50 mmol·L^-1, 3.65±0.07 g under 100 mmol·L^-1 and to 1.03±0.01 g under 150 mmol·L^-1 Cd²⁺ treatments. Similarly, chlorophyll (a+b) content mg·g^-1(FW) declined from 6.72±0.05 to 6.66±0.17, 6.02±0.15, 5.38±0.07 and 3.94±0.06, respectively. Proteomic techniques analyses showed that treating seedlings with 100 mmol·L^-1 Cd²⁺ altered over 50 protein species. 9 protein spots were identified via the MS/MS approach. The identified protein sports included: spot-1 (PWWP domain containing protein), spot-2 (AAA-type ATPase family protein), spot-3 (NB-ARC domain containing protein), spot-4 phosphoenolpyruvate carboxylase (PEPC), spot-5 (deoxycytidylate deaminase), spot-6 (maturase K), spot-7 (GRAS family transcription factor), spot-8 (resistance protein) and spot-9 puroindoline B (pin). These identified Cd2+ responsive proteins were possibly involved in DNA function modification (DNA methylation), energy metabolism, cell signal transduction, protein biosynthesis, gene transposition, intron splicing and defense response. This suggested that several protein types were responsive to Cd²⁺ stress. Proteome technique was applicable in studying physiological and biochemical mechanisms of adaptation and tolerance of plant to heavy metals.