Novel potato plants with enhanced cadmium resistance and antioxidative defence generated after in vitro cell line selection

Abstract

It is of interest to apply plant tissue culture to generate plants resistant to toxic effects of cadmium (Cd) on plant growth. Callus cultures were initiated from leaf explants of micropropagated potato plantlets (Solanum tuberosum L., cv. Iwa) for in vitro selection comprising 18 different Cd treatments varying in Cd exposure timing and duration. Plantlets regenerated from two different lines of Cd-selected calli, L9 and L11, were found to exhibit enhanced resistance to 218 μM Cd compared to control (source plantlets for leaf explants used to initiate callus cultures for Cd resistance). In response to 218 μM Cd, L11 plantlets had lower levels of lipid peroxidation and hydrogen peroxide than control and L9 plantlets. In addition, antioxidative enzyme activities in L11 were generally higher than control. L11 also had a higher level of proline than control.

Fig 1. A schematic summary of the sequence of major steps towards generation and characterization of Cd-resistant potato lines.

Fig 2. Growth of two in vitro-generated plant lines, namely L11 and L9, in the presence of 218 μM Cd compared to control.

A&B: Comparison of shoot heights from 90^o and 45^o views, respectively; C: a healthy green leaf of a L11 plantlet and a necrotic leaf of a control shoot; D: a root of a L11 plantlet; E: lack of root formation in a control shoot segment.

Fig 3. Differential growth responses (root length, shoot length and number of new leaves formed per plantlet) to 218 μM Cd of five Cd-selected potato lines selected from the first screening round after 20 days of culture.

Means having the same letter are not significantly different by Duncan’s multiple range test (p<0.05).

Fig 4. Differential responses to 218 μM Cd of 5 Cd-selected potato lines from the first screening round after 20 days of culture in relation to fresh and dry weights (FW and DW, respectively, in g per plantlet) of roots and shoots.

Means having the same letter are not significantly different by Duncan’s multiple range test (p<0.05).

Fig 5. Levels of reactive oxygen species, antioxidative enzyme activities and proline in the leaves (left-hand panels) and roots (right-hand panels) of control, L9 and L11 plantlets exposed to 0, 29 and 218 μM Cd for 7 days.

Upper and lower case letters are used for comparison among different treatments for the same line, and among different lines for the same treatment, respectively. Means with the same letter are not significantly different by Duncan’s multiple range test (p<0.05). The vertical bars show standard errors.