Soil adaptation of transgenic in vitro carrot plantlets

SUMMARYAdapting in vitro transgenic carrots to soil is the most crucial step preceding the field investigation of transgenic carrots. A low proportion of plants, around 0·20, acclimatize to soil (Hardegger & Sturm 1998) and thus prohibit the generation of high-expression carrot lines. In the present paper, a protocol for an efficient soil transfer is presented and the impact of carrot cultivar, soil substrate, tissue culture, and transformation process on transfer process is analysed. Somatic embryo germinants of Daucus carota cv. Rote Riesen 2 and Lobbericher Gelbe Futtermoehre showed a tremendous survival proportion – up to 1·00 – when transferred to their optimal soil substrate: sandy and loamy soil, with low content of macro and micro elements and a pH of 5·8. By optimizing the conditions described here, the proportion of soil acclimatized transgenic carrot plants of D. carota Lobbericher Gelbe Futtermoehre was increased from 0·1 to 0·87, and for the cultivar Rote Riesen from 0·09 to 0·67.

Uptake and Assimilation of Nitrate and Iron in Two Vaccinium Species as Affected by External Nitrate Concentration

Most Vaccinium species have narrow soil adaptation and are limited to soils that have low pH, high available iron (Fe), and nitrogen (N) primarily in the ammonium (NH4+) form. Vaccinium arboreum Marsh. is a wild species that can tolerate a wider range of soil conditions, including higher pH and nitrate (NO3-) as the predominant N form. This wider soil adaptation may be related to the ability of V. arboreum to acquire Fe and NO3- more efficiently than cultivated Vaccinium species, such as V. corymbosum L. interspecific hybrid (southern highbush). Nitrate and Fe uptake, and nitrate reductase (NR) and ferric chelate reductase (FCR) activities were compared in these two species grown hydroponically in either 1.0 or 5.0 mm NO3-. Nitrate uptake rate (on a whole-plant and FW basis) and root NR activity were significantly greater in V. arboreum compared with V. corymbosum. Iron uptake on a FW basis was also greater in V. arboreum, and was correlated with higher root FCR activity than was found in V. corymbosum. Increased Fe and NO3- uptake/assimilation in V. arboreum were reflected in increased organ and whole-plant dry weights compared with V. corymbosum. Vaccinium arboreum appears to be more efficient in acquiring and assimilating NO3- and Fe than is the cultivated species, V. corymbosum. This may partially explain the wider soil adaptation of V. arboreum.

Effect of External Nitrate Concentration on Nitrate and Iron Uptake and Assimilation in Vaccinium Species

Most Vaccinium species, including V. corymbosum, have strict soil requirements for optimal growth, requiring low pH, high iron, and nitrogen, primarily in the ammonium form. V. arboreum is a wild species adapted to high pH, low iron, nitrate-containing soils. This broader soil adaptation in V. arboreum may be related to increased efficiency of iron or nitrate uptake/assimilation compared with cultivated Vaccinium species. To test this, nitrate and iron uptake, and nitrate reductase (NR) and ferric chelate reductase (FCR) activities were compared in two Vaccinium species, V. arboreum and the cultivated V. corymbosum. Plants were grown hydroponically for 15 weeks in either 1.0 or 5.0 mm NO3 with 0.09 mm Fe. Root FCR activity was greater in V. arboreum compared with V. corymbosum, especially at the lower external nitrate concentration. However, this was not reflected in differences in iron uptake. Nitrate uptake and root NR activity were greater in V. arboreum compared with V. corymbosum. The lower nitrate uptake and assimilation in V. corymbosum was reflected in decreased plant dry weight compared with V. arboreum. V. arboreum appears to be more efficient in acquiring nitrate compared with V. corymbosum, possibly due to increased NR activity, and this may partially explain the wider soil adaptation of V. arboreum.