Investigação de possíveis obstruções sílico-aluminosas em tecidos condutores em Pinus Caribaea Var. Hondurensis relacionadas à senescência e morte de plantas

Abstract

Senescence (yellowing and needle drp) and death of mature plants has been observed in tropical pines forest stands established in the seventies in savannah areas of the Triângulo Mineiro and Alto Paranaíba (MG) regions. Previous studies showed a close relationship between this physiologic patterns with nutrient deficients. Also, it is known that the seeds used in the establish of forest presented great genetic variability, which is expressed on the diversity of plant performance, since part of them remains healthy while another part shows a decline and death process, with variable intensity. This study was conducted as a continuation of the research line, based on the hypothesis that polymers associated with silicon (Si) would be obstructing the tracheids, thus contributing for plant nutritional collapse. Segments of roots and apical shoots of plants apparently healthy (green needles), in different senescence stages (yellowing needles) and dead were collected. These samples were processed and dried in a critical point dryer and analyzed in a scanning electron microscope coupled with an X-ray microprobe. The presence of Si and aluminium (Al) in xylem and phloem tissues was observed on shoots and roots. However, no obstruction or the presence of any Si-Al body in the conducting tissues was found. Moreover, the presence of Si was associated with Al according to a relation Al/Si of 2.6. The data also revealed that the Si variation range was 1.5 times greater than that of Al.