Final answer:
Robert Hooke and Anton van Leeuwenhoek's observations of plant cells using microscopes contributed to the development of cell theory. Their work led to advances in plant breeding by allowing alteration of plants at the cellular level to create new varieties.
Step-by-step explanation:
The discoveries made by Robert Hooke and Anton van Leeuwenhoek using early microscopes had a significant impact on our understanding of plant cells and thus influenced the field of plant breeding during the scientific revolution. By observing the structures we now know as cells through his compound microscope, Hooke proposed that these 'honeycomb'-like structures were the building blocks of plant material. This revelation, described in his 1665 publication Micrographia, laid the foundation for cell theory, which posits that all living things are made of cells. Anton van Leeuwenhoek furthered this understanding with his superior lens-making skills, observing even smaller organisms like bacteria and human cells. This knowledge allowed future scientists and breeders to manipulate plant characteristics on a cellular level, leading to the development of new plant varieties with desired traits.